Polypropylene (PP)  block 50mm x 50mm - 10mm & 6mm Thick Black finish both have 12mm hole center.

Polypropylene (PP) is a versatile thermoplastic polymer used in a wide variety of applications

Polypropylene (PP) block 50mm x 50mm - 10mm & 6mm Thick Black finish both have 12mm hole center. 

use as spacers, between a truck chassis and tray, also called shims. 

Lightweight

Resistant to moisture, chemicals, and fatigue (especially bending and flexing)

Good electrical insulator

Tough and flexible

Recyclable (recycling code: #5)