All Berntsen bronze survey caps for rebar are orbital formed from silicon bronze alloy that won't chip, crack, or break. They feature the SureGrip™ plastic insulator that locks the cap tight on to the rebar or pipe and helps prevent dissimilar metal corrosion. They feature a deep hex socket that won't "wobble" when tapped on to the rebar.

A good survey cap for rebar or pipe must virtually eliminate dissimilar metal corrosion. What typically happens is that the survey cap loosens over a short period of time. This confirms metallurgical theory.  Aluminum is less "noble" than steel and an electrical current will actually flow from the aluminum (+) to the steel (-). Corrosion will occur in the anode (+) area of the battery like combination of metals in the presence of moisture (air or soil acting like an electrolyte).

Berntsen originated the SureGrip™ insulator/wedge which effectively isolates the survey cap from the steel and de-forms around the ribs of the rebar. The hex shape fills with the deformed plastic material and the survey cap is locked on with a super tight compression fit. Great force is required to remove the cap.