Unfortunately the website advertises some misleading products. I ordered a TRV adverised specifically as 10mm, there are also 8mm ones advertised. I really wanted a 10mm one, had looked for ages to find one. When it arrives, its just 15mm with a cheap reducer, exactly what i wanted to avoid. Turns out they only make 15mm TRVs but make out like theyve got all these different parts. They should just say, 'we only make one size, but we'll throw in a reducer for free.' Least you'd know where you stand. That being said, the company offer quick service and respond quickly and politely to emails. They offered a refund but its too late by the time you get the part, and i think they bank on you just making do.