Allen Keys
Browse used Allen keys for sale from riders across the UK. This category covers hex keys in the sizes bikes actually use — 2, 2.5, 3, 4, 5, 6, 8 and 10mm — in folding sets, L-shaped keys, T-handles and P-handles, alongside the T10, T25 and T30 Torx keys that sit next to them in most kits. It suits anyone adjusting a stem, seatpost, disc rotor or crank bolt at home.
What sizes of Allen key does a bike need?
Nearly every bolt on a modern bike takes 4, 5 or 6mm. A 3mm turns some derailleur and cable-clamp fittings, 2 and 2.5mm handle small grub screws and shifter covers, and 8mm turns pedal spindles and older crank bolts. A 10mm appears on some crank and axle fittings. Because Torx has replaced hex on rotor bolts, brake mounts and many stem faceplates, treat a T25 as part of the same set. If you buy one thing, make it a 5mm — it turns more bike bolts than anything else.
L-key, T-handle or folding set?
An L-shaped key gives the most leverage from the long arm and reaches into recesses with the short one, which is why most workshop sets are L-keys. A T-handle spins faster and lets you push straight down the bolt axis, so it's better for repetitive work and for bolts you need to feel — the trade-off is bulk and less leverage than a long L arm. P-handles combine both. A folding set is compact and cheap but the plates get in the way in tight spots. Ball ends let you drive a bolt at an angle, but only for finishing threads — start and finish tight bolts with the flat end, because a ball end concentrates load on a small area and rounds the socket.
What should I check on used Allen keys?
Look straight at the tip. The six corners should be sharp and square; if they're rounded off or the end looks slightly tapered, the key will slip in the bolt and start rounding bolt heads, which is a far more expensive problem than a new key. Check the ball end for chips or flat spots. Sight down the shaft for a bend — a twisted key has been overloaded and the metal is already compromised. On folding sets, check the pivot bolt is tight enough that the key doesn't flop while you're turning it. Surface rust on the shaft is fine; pitting at the working tip is not. Also count the set: the 4mm and 5mm are the ones people lose.
Are used Allen keys worth buying?
A full set of hardened keys costs little new, so used only makes sense for good ones — a Wera Hex-Plus set, Bondhus L-keys or Park Tool P-handles bought at half price is a genuine saving on tools that will outlive several bikes. A worn budget key is worth nothing regardless of price. Buy new if you're working on carbon parts, titanium bolts or anything at a stated torque, where a slightly rounded key can slip and damage a part worth far more than the tool. Complete sets in a holder are worth more than loose keys, partly because you can see what's missing. Check what else you need alongside them in hand tools — a set of screwdrivers for limit screws and a couple of wrenches covers most of what hex keys can't.
Do I still need Allen keys if I have a multi-tool?
Yes. A multi-tool's hex bits are short and set into a body that fouls on the frame, so you can't always get a straight line on the bolt, and the short handle makes it easy to apply uneven force. That's fine for a trailside adjustment and poor for a bench job like fitting a stem or torquing a crank. Keep the multi-tool in the saddlebag and a proper set on the bench.