Hexlox Insert 4 mm – Black
The Hexlox Insert 4 mm – Black is a small stainless steel anti-theft insert that turns any magnetic 4 mm hex bolt on your bike into a lock: a standard Allen key can no longer grip the bolt, and only your personally coded Hexlox Key takes the insert out again.
Why protect your bolts with Hexlox?
Blocks every Allen key. Once seated, the insert fills the hex socket, so standard tools have nothing to grip. 
Fits the bolts you already have. No replacement bolts, no drilling – the insert sits inside your existing 4 mm steel bolt, held by a small magnet. 
Personal key code. Every key and insert carries a 3-digit code; only parts with the same code fit together. 
Weatherproof. Stainless steel that stays in the bike all year round. 
Service in seconds. Take the insert out with your key, use a normal Allen key, then put it back.
Why your parts need it
Saddles, seatposts, stems and wheels are fixed with standard hex bolts – anyone with a pocket multitool can remove them in seconds. Most part thefts are exactly that: quick and opportunistic. The Hexlox Insert 4 mm closes that gap without changing how your bike looks or rides; the black finish disappears into dark components.
Where the 4 mm insert fits
The insert size equals the Allen key size of the bolt. A 4 mm insert is typically used on seatpost clamp bolts, stems and handlebar bolts. The highlighted points show where it is typically used.
Who is it for?
- Riders with a quick-to-steal seatpost. A 4 mm seatpost clamp bolt is the only thing between a thief and your seatpost and saddle.
- Owners of a premium stem or handlebar. Lock the 4 mm stem and faceplate bolts.
- City commuters. Whose bike stands outside for hours at the station, office or university.
Size guide and fit
| This insert | Bolts with a 4 mm hex socket |
|---|---|
| Bolt material | Steel (magnetic) bolts; aluminium, stainless or titanium bolts need a Hexlox steel bolt or the Hexlox insert for non-magnetic bolts |
| Saddle | 5 or 6 mm |
| Seatpost clamp bolt | 4 or 5 mm |
| Stem and handlebar bolts | 4, 5 or 6 mm |
| Quick-release wheel | Hexlox QR axle + 5 mm insert |
| Thru-axle or nutted wheel | Hexlox thru axle or Hexnut + 6 mm insert |
| In the box | 1 × Hexlox Insert 4 mm, key code card |
| Required | Hexlox Key with the same 3-digit code (sold separately) |
Frequently asked questions
Will the 4 mm insert fit my bolt?
Do two quick tests. If a 4 mm Allen key fits the bolt, the size is right. If a fridge magnet sticks to the bolt, it is steel and the insert will hold.
Can a thief pull it out with a magnet?
No. According to Hexlox the insert cannot be removed with a magnet, even an industrial one – the key and insert are a purely mechanical fit.
Do I need a key?
Yes. The Hexlox Key is sold separately and is needed to fit and remove the insert. Inserts and a key ordered together come with the same key code. Planning more parts later? Note your code and contact us.
How many inserts do I need?
One per bolt you want to protect. Count the bolts on each part – a saddle clamp, for example, often has one or two.
How do I keep it working?
If you ride all year in city grime, take the insert out now and then, clean the socket and add a drop of oil so nothing seizes.
No lock in the world is 100% secure. Hexlox stops the quick, opportunistic theft of parts – for the frame itself, always use a good frame lock and a fixed anchor point, as Hexlox recommends too. Hexlox was founded in Berlin in 2016 with one idea: bike bolts are already highly specialised, so instead of replacing them, build a lock that fits into the bolts you already have. Designed and made in Germany, Hexlox is sold through more than 500 bike shops in over 67 countries – worry less, ride more.About Hexlox