As far as I can tell there was 4 different small key molds.

Old Gem - 3 7/32 Guage (thick) -517 Micrometers(diameter)
New Gem - 3 12/32 gauge - 562 Micrometers
Gem Sandblast- 3 11/32 Gauge - 550 Micrometers
Gem Sandblast- 3 11/32 Gauge - 547 Micrometers

I believe this one is the Lkey mold.
New Big Gem - 3 12/32 Gauge - 562 Micrometers

*information from a Burt mold list. Circa 1950's but not sure of the date.