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ONGUARD

OnGuard Mastiff 3.5 ft Chain Lock with Integrated Key Lock – 10 mm Hardened Steel Hex Links (110 cm / 3.57 ft) – X2P Double Bolt Lock Head, Z-Cylinder Core, 5 Keys

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Availability: Only 5 left in stock, order soon!
Fulfilled by Amazon
Arrives Friday, Jul 10
Order within 3 hours and 59 minutes
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Size: 10mm x 3.5 ft


Features

  • High-Security X2P Lock Head: Integrated X2P Double Bolt mechanism locks both sides for superior resistance against pulling, twisting, and prying attacks.
  • Heavy-Duty 10 mm Steel Chain: Titanium-reinforced hardened steel hex links provide strong defense against cutting, leverage, and impact attacks.
  • Practical 110 cm Locking Length: 110 cm (3.57 ft) chain length provides flexible locking options around racks, poles, and fixed urban objects.
  • Advanced Z-Cylinder Protection: Precision locking core resists bumping, drilling, and picking for dependable anti-theft performance.
  • Complete Key Set Included: Comes with five laser-cut keys.

Description

The OnGuard Mastiff 3.5 ft Chain Lock delivers serious protection for bikes, scooters, and e-bikes in medium-to-high risk environments. The 110 cm (3.57 ft) chain is built with titanium-reinforced hardened steel hex links designed to resist cutting, prying, and leverage attacks. The chain integrates directly into a heavy-duty X2P Double Bolt Lock Head, securing both sides of the locking mechanism for exceptional pull resistance. A dual rubber housing helps protect frames and finishes from scratches while also improving durability and weather resistance. The advanced Z-Cylinder core adds protection against bumping, drilling, and picking attempts for dependable long-term security. Designed for riders who want strong yet manageable protection, this chain lock offers an ideal balance of durability, portability, and everyday convenience. Includes five precision laser-cut keys.

Brand: ONGUARD


Special Feature: Heavy Duty


Lock Type: Key Lock


Item dimensions L x W x H: 11.5 x 8 x 3 inches


Material: Rubber


Brand Name: ONGUARD


Recommended Uses For Product: Cycling, Security


Number of Pieces: 1


Included Components: ONGUARD 8020


Model Number: 45008020


UPC: 768661281328 768661280208


Model Name: 45008020


Global Trade Identification Number: 08


Manufacturer Warranty Description: 2 year manufacturer


Manufacturer: OnGuard


Unit Count: 1.0 Count


Manufacturer Part Number: 8020


Item Type Name: Bike Lock


Additional Features: Heavy Duty


Lock Type: Key Lock


Controller Type: Hand Control


Control Method: App


Smart Home Compatibility: Not Smart Home Compatible


Style Name: Modern


Color: Black


Shape: Square


Material Type: Rubber


Finish Types: Painted


Item Dimensions: 11.5 x 8 x 3 inches


Item Weight: 5.7 Pounds


Frequently asked questions

If you place your order now, the estimated arrival date for this product is: Friday, Jul 10

Yes, absolutely! You may return this product for a full refund within 30 days of receiving it.

To initiate a return, please visit our Returns Center.

View our full returns policy here.

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  • Financing through Apple Pay
Leasing options through Acima may also be available during checkout.

Learn more about financing & leasing here.

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Top Amazon Reviews

    • Solid. Bulky solid. Legit.
Size: 10mm x 3.5 ft
This lock is no joke. The chain is heavy and there is no denying that. The lock is a bit silly in my opinion. The key doesn’t easily slide in and it’s very ambiguous as to whether it’s locked or not (click feel when turning key). The key doesn’t come out when it’s unlocked - which is very clear - but I would rather have a more traditional @click - it’s locked” type of feel. ... show more
Reviewed in the United States on April 14, 2024 by Nathaniel P Molgren
    • Really solid lock.
Size: 6' x 3/8""
A touch heavy, still a great lock. LOVE the extra length. I carry mine in a basket so the weight does not bother me.
Reviewed in the United States on December 23, 2025 by Amazon Customer
    • So easy and quick to use!
Size: 10mm x 3.5 ft
I struggled to figure out how to use this the first time, because I thought there was a trick to turning the lock and removing the key. There’s no trick. Basically if the key is in the lock the lock opens. You can’t remove the key unless you lock it again. This is a rather genius way of making sure you don’t lose your key. Now that I understand it, it’s super simple to tie my bike up anywhere in just a few seconds. The chain is heavy duty, so this is not a fun thing to carry around (heavy). I keep it in a pannier on my bike, so it never really bothers me. Another option is to wrap it around the top tube several times and lock it in place while on the go. No need to keep it in a backpack. I got the smaller size, and that's more than enough length for securing my bike everywhere I go (unless you are tying it to a tree). It's a rather menacing looking lock, so unless someone is traveling with a saw, your bike isn't likely to become a target. I was tempted to buy some of the cheaper options, but I am SO SO glad I went with this one. I feel very confident about my bike being secure wherever I leave it. Definitely worth the money. Two year update: I've taken this with me to different states and countries and used it with different bikes I have purchased in different places. Its been rained on, dragged, packed in luggage, left in a shed, and I've never has issues with it, and no one has ever attempted to steal my bikes. I've oiled the lock like three times in two years. Its a winner. ... show more
Reviewed in the United States on November 10, 2024 by Faith H.
    • Heavy duty and just plain heavy! But very secure!
Size: 6' x 3/8""
Like carrying a tow chain. I will only use this when my bike needs to be left outdoors. Not something you’ll carry on a ride. But, it’s what I expected and definitely serves its purpose. Don’t buy it if you are expecting it to be light.
Reviewed in the United States on July 2, 2025 by Mike Tucson
    • Heavy but hardcore good
Size: 10mm x 3.5 ft
Great lock. Only reason i gave 4/5 is because it’s very heavy. Which means secure? Lock and keys work very smoothly and its big enough to both protect your bike or yourself:)
Reviewed in the United States on November 19, 2025 by Jbird
    • Heavy chain, scary padlock!
Size: 6' x 3/8""
The 10mm chain is substantial. The padlock size took me aback when I first unwrapped it. The lock mechanism is smooth and easy to use. I like that the lock has a rubber coating on the U portion. I was somewhat surprised by the amount of plastic sheathing on the lock, but it does appear sturdy. I bought an OKC noose chain to go with (my Scouting unit often goes on group rides to the movies, etc., so this extends the group coverage while we're inside). The OKC links are narrower, but do slide over the lock (displacing some of the rubber coating). The OnGuard chain is robust. I could slide the nice cover enough to check all the link welds which looked good. Hoping to get many an event-free year with this lock and chain. Nothing will deter a determined thief, but this will at least divert attention elsewhere. When we go away, the lock and chains are used to secure our bikes to the floor anchor. ... show more
Reviewed in the United States on July 23, 2023 by KCCjr
    • Construction is very good I am confident that it will deter any would ...
Size: 10mm x 3.5 ft
I have only had this for a little while but so far I am really impressed. Construction is very good I am confident that it will deter any would be thieves. On some chains that I read about before ordering this one a common complaint was the lock being hard to unlock, so far my lock opens smoothly with no problem. The main key is very nice with a light to help you unlock the chain in the dark. 4 extra keys come with the lock with the ability to order more if you need to which is very nice. I was a little apprehensive about carrying a bulky chain but it curls nicely under my seat and I don't really feel the extra weight. ... show more
Reviewed in the United States on August 26, 2017 by Stephen T Hammond
    • The Mastiff isn't for crybabies or wimps...
Size: 6' x 3/8""
...I was prepared for the size and heft of the chain, but it's the size of the lock that surprised me. The picture is a bit misleading; the lock has the size and heft to match the chain; this setup is massive and dense. I need this to protect a $1000+ e-bike; I do not want to lose it from some wire cutters on a $30 cable lock. I'd say it is about the limit you'd want to carry on a bike (mine will rest on the rack). Understandable that one would not want to carry it on a speedy road bike, but you have a big decision to make on security vs. weight. I find it stupid that one could neg this chain/lock because of the weight; you want "near" theft-proof protection but you want it thin and light; it's an impossible tradeoff, not gonna happen. The Mastiff will deter almost all thieves on looks alone; that's what I'm paying for. If I HAVE TO leave my e-bike alone and out of sight, the Mastiff is what I want on it to feel confident that my bike will still be where I parked it. You'll save a few pounds if you choose the shorter chain (and that is a good option if you just want a wheel and the frame secured), but I prefer the 6 footer to catch both wheels (especially that front motor wheel) and the frame. 10lbs of protection for peace of mind; i'll carry the weight. ... show more
Reviewed in the United States on November 28, 2016 by UnoDosAdios

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