These stands can be used for many purposes but they are best used for displaying Crystal Slabs. 

Our small size is what we recommend for ~1-2" sized (thin) slabs.
Our medium size is what we recommend for almost all of our medium/large sized slabs
Our large size is for only the largest of crystal slabs (~6"+)

Measurements:
Small: ~1.4"H x 1"W x 1.3"D, Gap for slab is ~.25" Deep.
Medium: ~2.2"H x 1.7"W x 2"D, Gap for slab is ~.4" Deep.
Large: ~2.65"H x 1.9"W x 2.35"D, Gap for slab is ~.6" Deep.