"I have brought quite a few plumbing bits from Screwfix just lately and have been very pleased but this coupler isn't the best. I purchased 2 for flexi pipes on hot and cold taps and tightend them both up using plumbers putty on the male threads. It didn't matter how much I tightened them up they both still dripped from the olive joint end. I ended up taking them apart again and noticed the olive just wasn't gripping the copper pipe. I finished off by putting PTFE tape over the olives then retiightening the nuts. Not sure this is good practice as I'm not a plumber but so far they have not leaked again."