Tube Clamp Connectors The clamping bores of GN 131 two-way connector clamps are mechanically machined and designed for construction tubes GN 990 or DIN 2391, DIN 2395 and DIN 2462 respectively. The standard version of the clamping screws are socket cap screws with hexagonal socket DIN 912. They can be replaced by clamping kits GN 911 GN 911.3 (article code see table of dimensions).