New, high quality corner cube (trihedral) prismĀ also called a retroreflector that will reflect light back to its origin regardless of the orientation of the prism face.
Note: This prism has a copper coated bevel with black overpaint.

Specifications:

Dimensions: 25.4mm diameter x 19mm deep.
Material: BK-7.
Scratch & Dig: 60-40
Flatness: 1/4 wave @633nm
Deviation: +/- 5″
Bevel: 0.2 x 45 deg.
Clear Aperture: >80 percent.