Have a thick rubber shim that every half hour slips around 1 cm or so. Trouble then is it's very hard to push up again,even after loosening boom clamp. They should make the shims of softer rubber to they grip the mast better. Also make them of narrower diameter would help also to reduce slippage. Is this a widespread problem with these shims.
Not with my NP booms and NP RDM adapators used on Simmer masts, nor Chinook Pro Alloy RDM adaptor on NP and Simmer masts nor my generic RDM adaptor used on an old Maui sails ali boom and Simmer masts.
Have you tried lightly roughing-up the mast in the boom grip area? Have you tried different RDM adaptors?
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.
Severne shims are excellent and fit Maui sail heads. Never slipped and only need minimal tension.
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.
Select to expand quoteejmack said..
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.
Agree. I use the Ezzy ones and never had them slip.
Select to expand quoteneedsalt said..
I have NP ones and have never had slippage, but maybe just lucky?
Agreed. When I had an SDM only boom and RDM masts I used Neil Pryde and No Limitz rubber shims and hd way less slippage than with an RDM boom now.
So much so, that I am thinking about going back to using a shim
so what are u using Pete?
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
In the last 5 years I have used Ezzy on a Chinook boom, Pryde on a Pryde boom and KA on a KA boom - never had a slippage issue
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.
i dont have rdm but on the my normal north masts i have to use a slim spacer to make the maui boom fit well and it does slip down i wouldn't blame bad technique because i think it slipping would more likely be the result of good technique not bad
I have a Powerex RDM too. Love the mast. Last summer I misplaced my shim, and instead of buying another one, I just went and bought an RDM boom. Best decision ever. No more fiddly shims, and the boom goes on easy, and is easy to adjust when rigged.
