Allen bolt sizes?

[sniff]

Can someone tell me how I get the size of a bolt? I know its 3.5cm long and I think it 6mm wide. So I need to get two of these and a few others and want to make sure I get these right.

[stuR]

Im not sure on what bolts are called, i have seen m5 and m6 before, perhaps a m6 is 6mm? But regardless, you can take existing bolts to an ironmongers to compare up and buy them there

[Galviniser]

Then it would be M6 x 35, what's the top look like, is it a bolt or an Allen cap head or dome cap?


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[rictus01]

Bolts for Jap bike (and many others) are generally discribed as M (for metric) and a number corresponding to the mm size in diameter of the threaded shaft, so an M4 would be 4mm, then you have the type, for allen bolts it's normally cap or button (square type or domed), the other dimension you'll need is length, for example you'd order am M4 x 50 (the 50 would be 50mm length).

beyond this and normally on bigger bolts; they have different thread pitches (smaller than M8 are standardized), for this you'll need a thread gauge to measure it, but an example would be M10 x 50/1.25; the 1.25 being the thread pitch.

HTH

Cheers Mark.

[sniff]

Thanks Rictus. Think mine are M6 350 and they are countersunk Allen head.

[sniff]

12866

[timwilky]

Technically those are not bolts. They are machine screws.

Difference? Well google says my understanding was wrong. I had thought the real difference between a screw and and a bolt was that a screw has threads the length of the shaft. But apparently is is simply down to use. A screw fixes into an internal thread whereas a bolt requires an external thread such as a nut into which to fasten.

[yorkie_chris]

If you ask for allen head you'll probably end up with SHCS
http://www.mjvail.com/holokrome/images/dd_shcs_metric.GIF


That one you put pic of is socket countersunk head cap screw
http://i00.i.aliimg.com/photo/v0/390366078/DIN_7991_hexagon_socket_countersunk_head_cap.jpg