The McAlpine 1 1/4" BSP Compression Nut S8B is a plumbing fitting made by McAlpine that is used to connect pipes in waste and drainage systems. The "1 1/4"" measurement refers to the diameter of the pipe that the fitting is designed to connect to. The "BSP Compression Nut" designation refers to the type of threading on the fitting, which is designed to connect to other components with BSP threading and has a compression fitting design. The compression fitting design allows for a secure and leak-free connection between two pipes, without the need for additional sealants or adhesives. The "S8B" model number likely refers to a specific variant or version of the fitting, although without additional context it's hard to say for sure. Overall, the McAlpine 1 1/4" BSP Compression Nut S8B is a specific plumbing fitting that may be useful in certain waste and drainage systems where a threaded connection with compression fitting design is required to connect pipes or other plumbing components. ・ Available in 1¼", 1½", and 2" sizes