Resin cast over an aluminum stalk. We do not want our range finders to bend and droop over during a really hot troop! (I have seen it happen to resin ones!). The mold was designed to cast the RF with the Aluminum in place for the top. You will need to drill the bottom of the aluminum and bottom cap to allow for what ever bolt system you decide. Sized to fit our Version 2.0 Deathwatch Helmet.