What are the center 8,10,11,14,19 and 28 blades denominated in?

Threads per inch. Those are the Whitworth blades, ie the 55˚ ones. To translate, since they word things a bit oddly: SAE/Imperial is measured in TPI, with a 60˚ thread angle. ie your 8-32 x 1" type screws. Whitworth/American/US is measured in TPI, and is basically the same as SAE except with a 55˚ thread angle and rouded crests. Metric is measured in the distance from thread to thread (the thread pitch), with a 60˚ thread angle. These are for your ISO screws. ie M4 course, M6 fine, etc.

Is this small enough to measure female thread sizes?

I don't have mine handy right now. but I think you can measure the inside thread pitch down to about 5/16", and 8mm. I haven't used mine yet, but the stampings on the individual blades don't appear very clear.

How are the gauge findings used for purchasing a screw ( an initial search doesn't find such details listed in screw descriptions on store sites ) ?

You will need to use this tool in conjunction with a chart showing the common SAE and Metric bolt/screw sizes. This tool will determine the number of threads per inch or mm. You will also need the diameter of your fastener before heading to the store. For instance the common threads for a SAE 1/4” coarse bolt is 20 TPI (threads per inch) - while a 1/4” fine bolt has 28 TPI. This set is for external threads. You keep comparing the various thread gauges in the set until you match your fastener - use that information along with the diameter of your fastener to make the final determination. The last bit of information you need would be the length of the fastener and the type of head. So a common 1/4” SAE bolt that is 2” long would be described as 1/4”-20 X 2.

One side is marked Whitworth and the other is marked Metrisch, but nothing points to which end is which.

One says "Metrisch" which is German for Metric. These have numbers in tenths or hundredths marked on each tong. The other side is standard (American) and have whole numbers on each tong, along with a "G". There's a middle section which are Whitworth threads - those are same threads per inch as Standard, but each tooth has a 55° angle (as apposed to the 60 degree on the teeth of the other thread types).

Brand	ChgImposs
Manufacturer	FLXDirect
Item Weight	1 g
Package Dimensions	8.4 x 3.5 x 1.5 cm; 1 g
Item part number	EPC_MEA_000
Are batteries included?	No

Metric & Imperial & US Screw Gauge SAE Whitworth 55 Degree & Metrisch 60 Degree Thread Pitch Gauge for Industrial Measurement

Description

Specifications

Reviews

Common Questions