The product is designed to fit a 1 5/8” NRS style tubing.  This product requires no holes to be drilled into the tubing but rather utilizes a universal NRS U-Bolt (supplied with the purchase).  Simply attach the SpinRx Anchor Arm Swivel Raft-U using the supplied stainless steel U-Bolt and Nylok nuts. We have received feedback from our SpinRx Swivel Pulley customers that they would like the rope attachment point to swivel like our pulley.  In our development efforts, we observed that allowing the anchor rope to swivel at the tie off point, the life of the rope is prolonged.