Specification No. 0 has the dimensions of the hook head of 1.5 x 2.8 mm.
Specification no. 2 has the dimensions of the hook head of 1.5 x 2.4 mm.
Specification no. 4 has the dimensions of the hook head of 1.1 x 1.7 mm.
Specification no. 6, the dimensions of the hook head of 1.1 x 1.4 mm.