Malco 28 Gauge Dampers feature 1/4 in. (6.4 mm) bearings, allowing bearing holes to be made in round duct with the use of a scratch awl. Squeeze pipe so that it is oval shaped. Insert damper into pre-punched bearing hole(s). Pipe will spring back to round when released. Secure with wing nut(s) provided. Damper may be adjusted with screwdriver or optional damper handle. Available with or without handles.