Metric Bolt Sizes Question

[VR6 South 0]

I am trying to replace some of the bolts on my C with stainless items. What's the best way to work out the size, can you do this by the size of the bolt head? ie 8mm head = dia??

 

Cheers

[V-Dubstar 0]

Thread sizes are determined by thread diameter, thread pitch, and thread length mate. If u measure the diameter of the thread (outside of the threads), you'll get the 'M' number (ie M6 is just under 6mm dia).

 

To measure the pitch, u'd need a thread pitch guage, something like this. This will then determine what the pitch of the threads are (so you'll get a final figure, say M6 x 1.25) with 1.25 being the thread pitch. This is the bolt size, then obviously u also need the length of the threads, measure this from the bottom end of the bolt UPTO the head of the bolt, NOT the whole bolt!

 

You'll then be left with M6x1.25x20mm (based on wanting 20mm of thread)

 

Try using these, they have a pretty good range of bolt sizes, with a good sample of head choices too! Never had any problems with them and they arrive quickly :D

 

Bolt heads are in no way a method of determining size bud! Hope this helps :)

[Supercharged 2]

All the thread pitches are on ETKA. Easiest way to check though is to take a bolt out and lay it against the new one and see if the threads 'mesh'

 

Most M6 and M8 bolts on the Corrado are all 'standard' pitch so I just bought a massive selection of these. Also try and get a load of M6 flange nuts as they look cool and also have a self locking surface. Also buy a load of spring washers and locking washers and pay attention to what ETKA says and what comes off the car as stainless stuff has a tendency to work loose compared to mild steel - different torque loadings / expansion coefficients etc

 

Gearbox / shifter type stuff is M7 and harder to get hold of.

 

The M10 and M12 bolts VW use are often fine threaded but these are mainly for brakes and suspension so you can't really use stainless becuase of strength.

[VR6 South 0]

That's great. Thanks for the links they also give the size of the heads, pitch etc which is a real help. I have purchased few replacement nuts and bolts from VW recently and most of them seem to be standard steel items and not even zinc plated. Thanks for the tip although I'm not intending using any stainless fixings on the suspension or brake components :)