Ground buss insulators are compression molded from fiberglass-reinforced thermo-set polyester, a bonded material with higher moisture and heat tolerance than plastic insulators, and with more mechanical strength to enable electrical installers to crank up closer height tolerances than with porcelain insulators, making them more suitable for ground bar and perimeter grounding applications 

3/8" Tapped holes on both sides 
1 3/4" Diameter 
2" Standoff (height)