From the Czech Republic.
Black enamel, available in all sizes from 000 to 7. With black-coloured heads.
Black enamel is the most commonly-used finish and provides good anti-corrosive properties under ordinary conditions.
When considering what is or isn't "ordinary" conditions, the most important consideration is humidity. If you are concerned at all about the definition of "ordinary", you might want to consider using stainless steel pins.
Insect pins have different coloured heads, with the heads being made of nylon (plastic). Choice of a particular colour of pin head can be based on individual preference, but also on the specimen being pinned, and the manner of displaying the specimen.
Some people prefer the appearance of pins which have black heads. Especially for specimens that are primarily dark/black as the pins are less obvious than the gold-headed pins under these conditions.
Size 000: diameter 0.25mm, length ca. 39mm.
Size 00: diameter 0.30mm, length ca. 39mm.
Size 0: diameter 0.35mm, length ca. 39mm.
Size 1: diameter 0.40mm, length ca. 39mm.
Size 2: diameter 0.45mm, length ca. 39mm.
Size 3: diameter 0.50mm, length ca. 39mm.
Size 4: diameter 0.55mm, length ca. 39mm.
Size 5: diameter 0.60mm, length ca. 39mm.
Size 6: diameter 0.65mm, length ca. 39 mm.
Size 7: diameter 0.70mm, length ca. 52 mm.
Size 7 pins are sometimes referred to as "railway spikes" because of their rather impressive size. They can be slightly more expensive than the little guys, depending on the supplier.
A word of caution: some display and storage cases may not accommodate the extra length of these "spikes". Most notably, size 7 pins are too long to fit California Academy drawers.