Gibraltar SC-GPR40C 40 Inch Curved Rack Tube 1-1/2" diameter tubes bent at 15 degrees The Gibraltar Curved Drum Rack Extension Tubes are 1-1/2" diameter tubes bent at 15 Caution: use only GRS clamps with curved bars The Gibraltar Curved Drum Rack Extension Tubes are 1-1/2" diameter tubes bent at 15 Caution: use only GRS clamps with curved bars