Uniflex, UniBack and UniHard are all covers that are designed specifically for use in the Unibinder M, Unibinder 8.2 and Unibinder 8.1.
SteelCrystal, SteelMatt, SteelBack and SteelBook are the equivilent covers designed for use in the Unibind XU138, XU238 and XU338. (also the previous ST series). All off the above covers will work in any Unibind binding machine. For instance the chart below shows the equivelent sizes of the SteelCrystal (clear covers) that can be used instead of the Uniflex covers in the Unibinder series.
Uniflex covers SteelCrystal or SteelMatt covers
The benefit to using the SteelCrystal over the Uniflex is that the SteelCrystal is avaliable in a compatible product which is on average 20% cheaper than the Uniflex covers. Please contact us for advice