Re: A thread about threads......

Posted by PackardV8 On 2011/3/20 7:24:57

Altho i understand metric/imperial can be confusing i'm not sure what your specific issues are. It can vary.

My advice is to obtain something know as a Drill Gauge. About 3 to 8 dollars US each. Get one in metric and one imperial. They are used for QUICK measuring of drill bit diameters but i use them for sizeing bolts too. Get STEEL drill gauges not plastic.

Also get a thread pitch gauge about 5 or 10 bucks. It measures the TPI THreads per inch.

Imperial nuts and bolts generaly come in FINE thread and Coarse thread.

e.g. a common 1/4 inch bolt can be either 20 threads per inch or 28 TPI. 3/8 bolts are 3/8-16 or 3/8 24.


There are some special application threads that are known as a machine thread where the TPI is kind of a bastard. These are usualy only used on hardened threaded parts such as valve adjuster screws or other similar applications.

Also get a Tap Drill chart. Most machine tool and bolt stores will give them away for free.