Original (new in wrap) WW2 era Armourers Headspace Gauge.
- SM 139 – Armourers, headspace, .064 in., No. 1
They are typically used for the SMLE, BREN and Vickers to measure firing pin protrusion. .064"
Info for use in rifles:
"Gauge SM139 is equivalent to a "GO" gauge and is mostly useable when re-barreling a rifle or fitting a new bolt head."
Info For Use in Vickers MMG:
"Steel, low limit. Inserted in the extractor lip of the lock and into the chamber."