Several models of the unertls. they make them all the way to 2" in Obj diameter. It depends on which one you have and which mounts you have.
Unertl is back in business so you might be able to google them now.
Also, you can ask on BR central under the 1000 yard forums and lot of shooters there can help.
Email or call Jerry Phillips in PA. He buys and sells old unertls. PJ480@aol.com
or (215) 757-5037