Mason, the world's lightest Sold Secure Diamond rated bike lock, now available in compact 140mm or 180mm triangulated shackle lengths, and long 220mm or 300mm pentagonal shackle lengths. The compact 'mini-D' configuration is ideal for securing a single bike in theft prone areas. The high level of security is achieved by use of a unique triangulated 17mm thick shackle for the best strength to weight ratio. The Longer Mason locks adopt a complex 15.3mm thick patented pentagonal hardened steel shackle which is also the widest of its kind, ideal for securing multiple bikes. Every Mason lock features a double deadbolt crossbar locking mechanism for protection against twist attacks and an anti-drilling key cylinder. Seatylock have ensured lasting durability by using rust free hardened steel and a rattle free dampened design. Mason is ideal as a theft deterrent for longer duration security in city centres and other locations where stealing a bike may go completely unnoticed. Other suitable applications include additional home security used in conjunction with a ground anchor in the event of a garage break in, and higher value protection for e-bikes or motorbikes. Don't be an easy target, Seatylock for the bike you love!
Mason, the world's lightest Sold Secure Diamond rated bike lock, now available in compact 140mm or 180mm triangulated shackle lengths, and long 220mm or 300mm pentagonal shackle lengths. The compact 'mini-D' configuration is ideal for securing a single bike in theft prone areas. The high level of security is achieved by use of a unique triangulated 17mm thick shackle for the best strength to weight ratio. The Longer Mason locks adopt a complex 15.3mm thick patented pentagonal hardened steel shackle which is also the widest of its kind, ideal for securing multiple bikes. Every Mason lock features a double deadbolt crossbar locking mechanism for protection against twist attacks and an anti-drilling key cylinder. Seatylock have ensured lasting durability by using rust free hardened steel and a rattle free dampened design. Mason is ideal as a theft deterrent for longer duration security in city centres and other locations where stealing a bike may go completely unnoticed. Other suitable applications include additional home security used in conjunction with a ground anchor in the event of a garage break in, and higher value protection for e-bikes or motorbikes. Don't be an easy target, Seatylock for the bike you love!
in 2 offers
The lowest price for Seatylock - Mason 300 U-Lock right now is $139.90 at Seatylock Australia, compared across 2 retailers.
The all-time low was $139.90 on 31 July 2025. That's the lowest price we've ever tracked — a great time to buy.
Prices last updated 8 May 2026.
Seatylock - Mason 300 U-Lock
Mason, the world's lightest Sold Secure Diamond rated bike lock, now available in compact 140mm or 180mm triangulated shackle lengths, and long 220mm or 300mm pentagonal shackle lengths. The compact 'mini-D' configuration is ideal for securing a single bike in theft prone areas. The high level of security is achieved by use of a unique triangulated 17mm thick shackle for the best strength to weight ratio. The Longer Mason locks adopt a complex 15.3mm thick patented pentagonal hardened steel shackle which is also the widest of its kind, ideal for securing multiple bikes. Every Mason lock features a double deadbolt crossbar locking mechanism for protection against twist attacks and an anti-drilling key cylinder. Seatylock have ensured lasting durability by using rust free hardened steel and a rattle free dampened design. Mason is ideal as a theft deterrent for longer duration security in city centres and other locations where stealing a bike may go completely unnoticed. Other suitable applications include additional home security used in conjunction with a ground anchor in the event of a garage break in, and higher value protection for e-bikes or motorbikes. Don't be an easy target, Seatylock for the bike you love!
Mason, the world's lightest Sold Secure Diamond rated bike lock, now available in compact 140mm or 180mm triangulated shackle lengths, and long 220mm or 300mm pentagonal shackle lengths. The compact 'mini-D' configuration is ideal for securing a single bike in theft prone areas. The high level of security is achieved by use of a unique triangulated 17mm thick shackle for the best strength to weight ratio. The Longer Mason locks adopt a complex 15.3mm thick patented pentagonal hardened steel shackle which is also the widest of its kind, ideal for securing multiple bikes. Every Mason lock features a double deadbolt crossbar locking mechanism for protection against twist attacks and an anti-drilling key cylinder. Seatylock have ensured lasting durability by using rust free hardened steel and a rattle free dampened design. Mason is ideal as a theft deterrent for longer duration security in city centres and other locations where stealing a bike may go completely unnoticed. Other suitable applications include additional home security used in conjunction with a ground anchor in the event of a garage break in, and higher value protection for e-bikes or motorbikes. Don't be an easy target, Seatylock for the bike you love!
Last updated at 08/05/2026 10:30:12
Mason 300 Bike U-Lock | Sold Secure Diamond
Delivery $9.90
Seatylock - Mason 300 U-Lock inc Bracket
Free delivery between 14–19 May
originally posted on seatylock.com
I recently purchased 2 fat tire e bikes for my wife and I. It was a pain trying to find a lock that would work with them given the 4inch fat tires. After days of research (countless YouTube videos) I came across the Mason 300 lock. I really liked the design and the fact that it had a diamond bike rating from sold secure. Coupled with the fact that I could mount the locks to our front forks, I pulled the trigger and bought two. They both arrived quickly and very well packaged. They work perfectly on our fat tire bikes in locking the tire and frame to bike racks. I purchased two mounts and have them installed on our front forks to store the locks when we're not using them. Highly recommend these locks. Especially since they are the biggest diamond bike rated u locks I ... MoreI recently purchased 2 fat tire e bikes for my wife and I. It was a pain trying to find a lock that would work with them given the 4inch fat tires. After days of research (countless YouTube videos) I came across the Mason 300 lock. I really liked the design and the fact that it had a diamond bike rating from sold secure. Coupled with the fact that I could mount the locks to our front forks, I pulled the trigger and bought two. They both arrived quickly and very well packaged. They work perfectly on our fat tire bikes in locking the tire and frame to bike racks. I purchased two mounts and have them installed on our front forks to store the locks when we're not using them. Highly recommend these locks. Especially since they are the biggest diamond bike rated u locks I could find that would work on our bikes.
originally posted on seatylock.com
I bought the Mason 180 as the main lock for my Trek Dual Sport bike, and on arrival was blown away by the quality of this thing. The key turns smoothly, the lock opens and shuts nicely and it isn’t near as heavy as other locks of the type. I’ve seen complaints about the zip ties that come with the mount for this but I found they worked really well (even after my dog chewed halfway through one, leaving it held on by only 1.5.Definitely recommend the mount too, but mounting was my only disappointment with this thing. I have a decently large frame bike and there is nowhere on my inner frame I can mount this while also having a water bottle mounted. I found most of the rest of the recommended mounting angles awkward or in the way of body motion while biking, ... MoreI bought the Mason 180 as the main lock for my Trek Dual Sport bike, and on arrival was blown away by the quality of this thing. The key turns smoothly, the lock opens and shuts nicely and it isn’t near as heavy as other locks of the type. I’ve seen complaints about the zip ties that come with the mount for this but I found they worked really well (even after my dog chewed halfway through one, leaving it held on by only 1.5.Definitely recommend the mount too, but mounting was my only disappointment with this thing. I have a decently large frame bike and there is nowhere on my inner frame I can mount this while also having a water bottle mounted. I found most of the rest of the recommended mounting angles awkward or in the way of body motion while biking, fortunately my bike has a back rack mounted on it and I was able to mount the lock to that instead.Overall, great lock at a great price. Just check the measurements against your fame before buying for mounting reference!
originally posted on seatylock.com
Purchased the U-lock for use on Segway Ninebot E45 scooter and it works great for locking around either the stem/folding mechanism.Tried out some of the local bike parking spots over the weekend without issue.Key highlights of the design are being lower weight compared to many competing locks and extra level of security from the dual shackle locking design.The automatic lock cover feature is pretty slick and I imagine will add to long term reliability of the U-lock.
Mason 300 Bike U-Lock | Sold Secure Diamond
Delivery $9.90
Seatylock - Mason 300 U-Lock inc Bracket
Free delivery between 14–19 May
I recently purchased 2 fat tire e bikes for my wife and I. It was a pain trying to find a lock that would work with them given the 4inch fat tires. After days of research (countless YouTube videos) I came across the Mason 300 lock. I really liked the design and the fact that it had a diamond bike rating from sold secure. Coupled with the fact that I could mount the locks to our front forks, I pulled the trigger and bought two. They both arrived quickly and very well packaged. They work perfectly on our fat tire bikes in locking the tire and frame to bike racks. I purchased two mounts and have them installed on our front forks to store the locks when we're not using them. Highly recommend these locks. Especially since they are the biggest diamond bike rated u locks I ... MoreI recently purchased 2 fat tire e bikes for my wife and I. It was a pain trying to find a lock that would work with them given the 4inch fat tires. After days of research (countless YouTube videos) I came across the Mason 300 lock. I really liked the design and the fact that it had a diamond bike rating from sold secure. Coupled with the fact that I could mount the locks to our front forks, I pulled the trigger and bought two. They both arrived quickly and very well packaged. They work perfectly on our fat tire bikes in locking the tire and frame to bike racks. I purchased two mounts and have them installed on our front forks to store the locks when we're not using them. Highly recommend these locks. Especially since they are the biggest diamond bike rated u locks I could find that would work on our bikes.
I bought the Mason 180 as the main lock for my Trek Dual Sport bike, and on arrival was blown away by the quality of this thing. The key turns smoothly, the lock opens and shuts nicely and it isn’t near as heavy as other locks of the type. I’ve seen complaints about the zip ties that come with the mount for this but I found they worked really well (even after my dog chewed halfway through one, leaving it held on by only 1.5.Definitely recommend the mount too, but mounting was my only disappointment with this thing. I have a decently large frame bike and there is nowhere on my inner frame I can mount this while also having a water bottle mounted. I found most of the rest of the recommended mounting angles awkward or in the way of body motion while biking, ... MoreI bought the Mason 180 as the main lock for my Trek Dual Sport bike, and on arrival was blown away by the quality of this thing. The key turns smoothly, the lock opens and shuts nicely and it isn’t near as heavy as other locks of the type. I’ve seen complaints about the zip ties that come with the mount for this but I found they worked really well (even after my dog chewed halfway through one, leaving it held on by only 1.5.Definitely recommend the mount too, but mounting was my only disappointment with this thing. I have a decently large frame bike and there is nowhere on my inner frame I can mount this while also having a water bottle mounted. I found most of the rest of the recommended mounting angles awkward or in the way of body motion while biking, fortunately my bike has a back rack mounted on it and I was able to mount the lock to that instead.Overall, great lock at a great price. Just check the measurements against your fame before buying for mounting reference!
Purchased the U-lock for use on Segway Ninebot E45 scooter and it works great for locking around either the stem/folding mechanism.Tried out some of the local bike parking spots over the weekend without issue.Key highlights of the design are being lower weight compared to many competing locks and extra level of security from the dual shackle locking design.The automatic lock cover feature is pretty slick and I imagine will add to long term reliability of the U-lock.
I haven't used it yet (still haven't bought a new bycicle), but it looks and feels very strong and solid.The delivery was super fast: less than 3 days to another continent - the fastest delivery I ever had!And the price is really fair, too.Great job, guys, definitely recommended!
I purposely wanted a lock with small inner dimensions to minimize air space inside the lock and deter against prying attacks. This lock is exactly what I was looking for and is big enough to fit around my bike frame and bike racks/parking meters/posts in San Francisco while leaving a minimal amount of air space inside the lock. Haven't had the lock tested yet luckily but it seems to be made of high quality materials with good craftmanship. Also extremely light for a gold-rated lock. I did a fair amount of research on bike locks after having my last bike stolen using a pry attack against my u-lock and settled on the seatylock plus hexlox for my wheels.
What I like about this mounting bracket is that the U-lock stores quickly and easily, although I did augment the bracket with a Velcro strap on to hold the lock to the frame on the other end.I like the Pentagon 300 u-lock that I bought (so far). What I don't like about its mounting bracket is that it uses a strap, which stretches over time and if you cut the strap after installation it is very hard to try and get it tight on the bike frame again. Why Seatylock would use this flawed bracket mounting design is a mystery to me because a conventional bolt-on bracket would be much better (that's what my other u-lock brand uses and it's never come loose.)
We bought the smallest Mason for our 11-year-old son to lock his bike at school. It is compact enough to carry in his backpack and is easy to lock. Previous lock used had problems with the key breaking and wearing out. We are not afraid with the Mason for this to happen. The mechanism is foolproof and with 3 keys, you cannot get wrong.
Absolutely happy with the Mason 180 lock - soft covering saves bike from scratches, key can't fall out from the lock in open condition + secure, and the most awesome feature for me is that when both parts are connected but the lock is not in closed condition - the lock stays as one! It can be locked with one hand - thats super for me!I like that 180 size allows to use lock with different parking stations, in case of narrow tubes on the station I can lock the frame and the back wheel which allows me not to use line if I have to leave my gravel for a short time.Thanks to seatylock for good lock, I enjoy using it! Thanks for the answering my questions and fast shipping!This is a great lock that you be proud to use!
Seatylock Mason U-locks have all earned the highest Sold Secure Diamond rating along with only a few of the top models from bigger brands that are much heavier and way more expensive. Mason model numbers refer to the inside length in mm. The Mason 140 & 180 are 85 mm wide inside while the 220 & 300 are 115 mm wide.I chose the 180 because it fit within my frame along with a bottle cage and tire pump with enough room to easily mount and remove it from the bracket attached to the seat tube.Considered a compact U-lock, the Mason 180 is just big enough to attach one wheel and part of the frame to a post with no room for a thief to get in with large wrecking tools. Otherwise it will fit around most posts and just one tube, but you should also carry a good foldable lock, ... MoreSeatylock Mason U-locks have all earned the highest Sold Secure Diamond rating along with only a few of the top models from bigger brands that are much heavier and way more expensive. Mason model numbers refer to the inside length in mm. The Mason 140 & 180 are 85 mm wide inside while the 220 & 300 are 115 mm wide.I chose the 180 because it fit within my frame along with a bottle cage and tire pump with enough room to easily mount and remove it from the bracket attached to the seat tube.Considered a compact U-lock, the Mason 180 is just big enough to attach one wheel and part of the frame to a post with no room for a thief to get in with large wrecking tools. Otherwise it will fit around most posts and just one tube, but you should also carry a good foldable lock, chain or cable (at least 10 mm thick) if suitable posts are not available and also to secure removable parts like wheels and the saddle.The shackle is hardened steel with a triangular profile for the 140 & 180 and pentagonal for the 220 & 300 and is thick enough to stop a bolt cutter and really slow down an angle grinder. The locking bar is steel, reinforced where the shackle is secured at both ends by a spring-loaded mechanism that prevents it from rattling and falling out when unlocked. The pick-resistant lock cylinder has a spring-loaded dust cover. The optional bracket can be mounted in various locations on the bicycle, attached by 2 plastic hose clamps. It has a push-button lock and is snug enough to resist vibration.Shipping is free in the U.S. The shipping cost to me in Canada was mostly offset by the fact that no sales or import taxes were charged. You can contact the Seatylock site for prices and availability. Even if it may take a few weeks to get the Mason size you want, it will be well worth the wait.
Mason 140/180 locks are a relative joy to use. The 140 has been just enough in all situations so far with my steel-framed road bike. Rigid & grippy, no wobble on Seatylock mount, and a significant bit lighter to make these next level products to own. I do wish that it had been made more clear that (3) keys are included, as I had purchased as many spares again with the lock order and at a very high cost. Gotta make some time to follow up on that ~ No time for photos of this type either, but you get the picture -
