How to find out the bolt head size?

(2011-06-17 14:20:26) 1. Michael C Says: From a helm's manual, a bolt is listed as 10x1.25m
44 N.m (4.5 kgt.m,
33 tbf.frl

How do I know which wrench size to use on this bolt? From the internet, I found out it is actually 14mm.

But nothing ever says in the helm's to use a 14mm wrench....!

Thanks.2. Bertsta Says: M10 refers to the diameter of the threaded part of the bolt.

M means it's metric. 10 is the diameter in mm

1.25 is the thread pitch. This is the distance between each complete thread, expressed in mm.

The size of the bolt head isn't really relevant to it's purpose and varies between manufacturers, so it's not usually quoted. The thread diameter is what gives the bolt it's strength and this is what an engineer needs to know when choosing a bolt for a particular application. That's why you only see that dimension and the pitch quoted.

Typically in this size range, the bolt head is 1.5 or 2mm wider on each side of the thread, so an M10 bolt normally has a 13 or 14mm head. Use the wrench that fits when you get the bolt in your hand. Measure across the flats or just try different size wrenches on it.3. BEA Says: You answered your own question.

Repair manuals do not list bolt head sizes. Even top of the line factory service manuals don't show the head size.


You figure it out when you get to it.4. clncarplz Says: Measure across the head from 1 flat side to the other flat side. If it measures 14mm then the 14 wrench will fit it.5. Bud Says: Try different wrenches until you find the correct size! Tag: How to find out the bolt head size?