If you know that the windsurfer is a slalom sailor or free rider, these are perfect product for gift. You can chose the harness or impact vest the same way you would chose a t-shirt size. Chose the extension in SDM 48 from the Alu+ Double Pulley Extension, and from the Carbon+ pro boom the 170 size. You wont go wrong! Fin bag or Adjustable Outhaul set have one size, and will be loved by anyone.