21ft headstay length, 1/8inch max wire, 1/4inch turnbuckle. CDI Flexible Furler is used on daysailers as well as offshore passage makers, monohulls and multihulls. It is used by production boat builders and is also great as a retrofit. The flexible luff extrusion makes it the best choice for trailerables. Whether large or small, your cruising boat or daysailer should have a furling system. Going forward on any size boat is potentially wet and often dangerous, particularly if your crew is inexperienced. Changing sails as the wind comes up is not a lot of fun! The Flexible Furler can be used to both furl and reef your sail in any wind condition. CDI has eliminated expensive features only hard-core racers demand, thereby increasing the system's reliability while lowering the cost. As proof of the success of this design, Practical Sailor reports 100% of Flexible Furler owners surveyed would buy their Flexible Furler again if they had the choice. We are very pleased with these survey results since CDI was the only major furler manufacturer to receive that level of owner endorsement. The sizing for the CDI flexible furler is based on your headstay length, maximum wire diameter and turnbuckle size.