Barbed Secured—The ridged barrel makes these inserts even less likely to split hardwood than pronged inserts. They're often used in wood that has been cut across the growth rings.

Steel—Best for dry environments since moisture will cause these inserts to rust.

Black-Oxide Steel—These inserts are often chosen for the dark, matte appearance. They're best for dry environments since they can rust when exposed to moisture.

Zinc-Plated Steel—A step up from plain steel, the plating withstands occasional exposure to moisture.