Tuning Hammer with iron grip for oblong tuning pins for early keyboard instruments

Tuning hammer with iron grip, T-lever Rectangular hole for wrestpins with flat head (oblong) tuning pins for early keyboard instruments

Size I (1) = 2.9mm x 6.0mm
Size II (2) = 3.4mm x 6.5mm 
Size III (3) = 3.9mm x 7.0mm 
Size IV (4) = 4.4mm x 7.5mm

A = tuning-key size
Ø = for wrestpin-diameter
A               Ø             L x H         O /    U x B
I             3.0 - 3.5     72 x 90     1.4 /  2.9 x 6.0
II            3.5 - 4.0     72 x 90     1.9 /  3.4 x 6.5
III           4.0 - 4.5     92 x 90     2.4 /  3.9 x 7.0
IV           4.5 - 5.0     92 x 90     2.9 /  4.4 x 7.5

Reference : V then size number