For labs using solvents incompatible with polycarbonate, 4 ml polyethylene vials are a practiced alternative. Resistant to many solvents that melt polycarbonate, these cost effective PE Vial Sets are suitable for most small seeds and animal tissue. PE vials are relatively pliable compared to polycarbonate vials and are not as effective when used on large, hard samples like corn kernels. Vials work best with 3/8" Stainless Steel Grinding Balls and 5/16" Stainless Steel Grinding Balls. A case comes complete with 240 polycarbonate vials.