this Tri-Glide Buckle connects the headgear straps at the back or top of the head for easy adjustments on several Fisher and Paykel masks including the Opus 360 (HC482) Nasal Pillows CPAP Mask, Forma (40047X), FlexiFit 431 (HC431) and FlexiFit 432 (HC432) Full Face CPAP and BiPAP Masks.