I have NP ones and have never had slippage, but maybe just lucky?

The shim I have is an expensive one but will try the NP if I can find one. If you use a high boom with short lines it tends to pull the boom down more which could be the problem.

Never had a Ezzy (no limits) shim slip. They are a softer rubber. Only issue with them is they could be longer as the don't fit some of the longer boom clamps. Easy enough fix though.

As above. Total quality, never slips.

I got a severne metal boom its RDM only (didn't realise until i bought it). Haven't tried it yet but it looks the business

From the responses i don't think it's the RDM shim that I'm using more my bad technique. It's a powerex shim,quite thick,weighs 125g,heard from someone in the Windforce shop they are the best

All my booms slip,period,just with a rdm shim on so much harder to reset! Anyway going to start using the shim on my Sdm masts for added protection. I tried it once and it does fit sdm masts too,can't remember if it slipped or not on the sdm, but being a tighter fit hopefully not.

Try changing the rope in the front end, old rope can sometimes stretch.