This kit contains all seals needed for rebuilding a leaking air spring of a BOS Idylle fork. It also contains a valve core for the fork top cap. 
 
Please note: this kit replaces the seal between the brown and red anodized sleeve threads with a very slightly thicker o-ring than the stock to achieve more reliable performance. Of the two very similar sized o-rings, use the thicker one for sealing the threads between the sleeves and the thinner one to seal against the stanchion tube at the top of the air spring assembly. 
 
Service tip: Fox p/n 803-00-147 - Kit: Shaft Clamps, 07 FORX, Set #2 (32 X Body, 36, 40 Forx) can be used to clamp the brown anodized sleeve and a strap wrench can be used to unthread the red sleeve. 12 mm shaft clamps are also necessary for the job, for which a Park Tool AV-5 is the most easily available tool (ensure the 12 mm clamping surface is pristine on this tool if it is used for the fork service).