Metric and Imperical Bolt

Only using a thread gauge.

Back in the 70s Marconi insisted that all metric screws, nuts etc were coloured light blue - it worked extremely well.

I've still several boxes of fastners from that company all coloured light blue!!

John.

The markings will help

Here is a quick reference

Bolt markings

There are marks on the heads of bolts. These indicate the bolt grade. Imperial bolts are marked with lines from the edge of the bolt towards the center. Metric bolt grades are numbers. Low grade bolts may have no markings at all. Then its necessary to measure them. Thread gage will do the trick.

I usually use calipers on the thread diameter; i.e: M10 screw will measure ~0.385", too big to be 3/8", conversely the 3/8 screw will measure ~ 9.4mm, much too small to be M10.

Only tough one here is M8-5/16, these you'll need the pitch gauge for.

Why don't you buy a metric rule, that way you don't have to use conversion tables!

Spencer.

A thread gage is the most sure way to tell. I use a simple (and cheap) plastic one called a GAGE-IT hardware gage. These are made in the USA (imagine!) by Armour Technologies, Inc., Media, Pennsylvania. Don't know if they have a website... It has screws and bolts, nuts, drill, rod, wire, and tube, pipe & tubing, nails, angles, and all sorts of rulers and conversions printed in the spaces (both sides) between. Not bad for a 4"x8" piece of plastic!

Don't you mean 100mm x 200mm piece of plastic?

Errr...110mmX215mm eggshelly...

Get a catalog from Fastenall, look at the head, use a set of calipers, have a nut of known thread type and pitch, use a pitch gage....

Travis