The different types of corset busks:

The most common type of corset busk available today. Steel with a white coating to prevent rust. Most often with silver closures but can be found with brass clasps as well.

Made of heavy duty un-coated steel. The wider "spoon" base curves inward twords the abdomen. 

The spoon busk was most popular in the 1870's and afterward for "abdominal" corsets worn for more tummy control.

Made of heavy duty un-coated steel. The steels are wider and heavier

The Tapered Busk

or Conical Busk

Strait flat busk on which the bottom is significantly wider than the top. Has no curves or bends. Commonly used in 1905 - 1920's corsets. Uncommon to find for sale today. Most often made of un-coated steel with dipped ends though was often paper wrapped as well.

A standard busk enclosed in a paper covering.