Never change a winning horse

A new collar from my "classic" model: padded collar in hazel (outside) / caramel (inside) combination, with 3/4" (19 mm) stainless steel oval buckle, corresponding to a size M in my new size table.

This is the full size table:
XS is up to 12" (30.5 cm) at its central hole with 1/2" (12 mm) fittings;
S is up to 16" (40.5 cm) with 5/8" (16 mm) fittings;
M is up to 20" (51 cm) with 3/4" (19 mm) fittings;
L is up to 25" (63.5 cm) with 1" (25 mm) fittings;
XL is over 25" (63.5+ cm) with 1" (25 mm) fittings.