Compression Washing Machine Valve Without Check Valve 15mm x ¾" (51231)

That's because it is 3/4 BSP (British Standard Pipe) which is 26.44 mm (1.041") diameter. The size was originally based on the inside diameter, measured in inches, of a steel pipe for which the thread was intended. i.e. a pipe with a nominal 3/4" bore has an outside diameter of 1.041" which is threaded

Hello, Thank you for your enquiry. Plastic can be attached to compression fittings without problems. Just make sure you put an insert into the end of the plastic pipe to strengthen it and then tighten the fitting as normal. Thank you for using Q&A.

Hello Chalkwah, No, these are not suitable for use with potable water. Thank you for using Q&A

Hello Antena, Unfortunately this isn't the product that your looking for and we currently don't sell the correct item to join your two lengths of hose. Thanks for using Screwfix Q&A.