Always use push fit reducer rather than internal they never leak saves time and money best thing since sliced bread
Easy to order on line, quick response on collection, a small part doing a big job on my heating system.
Takes a lot of force to get 10mm pipe seated through the locking washer.. conversely, it will take a lot of force to remove, so the joint should be good for as long as the o-ring lasts. JG speedfit reducer is so much easier to install when dealing with short pipe lengths and perhaps wet hands that make the force required so hard to achieve.