Greetings, I have a Schaefer CF 500 snap furler on my 135% head- sail. It takes a number 5 luff tape sewn onto the sail and the whole unit snaps over top the existing head-stay without any modifications. It works flawlessly for me. I also have a foam luff sewn in to assist with proper reeefing. You can research the specs on the net or view at west marine. Bruce, s/v cerulea M17 32