Probably the biggest diffrence is the outside diameter of the shaft. Two prong rest will usually have an alluminum rest and a diffrent carbon rest due to this diffrence.
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Same with the WHISKER BISQUIT--the one for alum. has a larger hole but for me the the alum. style works the best with my carbon arrows---2315's still don't fit the bisquit because it's only rated for arrows up to 22 and 23 is too tight!
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