The Fisher & Paykel Aclaim 2 Headgear Strap is designed specifically for the F&P Aclaim 2 nasal CPAP mask. It's available in one size only, and is made of breath-o-prene material. Per the manufacturer, this part has been replaced with part 900HC429. If you order the product listed on this page you will receive 900HC429 since Fisher & Paykel now consideres 900HC429 to be the headgear strap for the Aclaim 2 mask. The 900HC429 part does not have a strap piece that goes over the top of the head from front to back, so there's no longer a tube retainer as part of the headgear strap.