Get yourself a step drill bit which is likely to be easier to open up a hole.

This has been my defacto solution in the past Pardon our interruption... but same principle. 4 months on and some recent rain how has this solution been holding up?Just my input FWIW. As an Engineer who’s worked on ‘liquid/air systems’ in my career from Low Pressure domestic water and gas, to fully automated High Pressure hydraulic system circa 3200 psi, when I fitted my ARB Baserack I massively over thought the ‘will it leak’ paranoia.
Then in a moment of clarity I just said ‘used the tried and tested principles you used in the above systems to great effect and keep it simple!!’
For roof rail, roof rack etc fitting that bolts into the existing roof mount threads I would simply use a good quality rubber spacer, or flat seal to suit your application and use some good quality liquid PTFE.
I rate this stuff. I use it on LP water and in a few minutes it forms a W/T seal. I used this on my roof rack bolts along with supplied ‘rubber pad’ from ARB and no issue. Also used it on other friends VW roof blank bolts as a precaution and 18 months later they too say previously leaking bolts now cured.
We are all guilty of overthinking it sometimes ( jeeeeeez. I’m the worst) but often a simple proprietary solution with less points of failure is best.
just my ‘go to’. HTH
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M6 x 1.0Thanks I've ordered a set of sealing bolts anyhow, but it would be kinda nice to refit the roof rails, even if their display purposes only. I was just worried I might wreak the female threads inside the roof space using a threaded bar with the wrong thread pitch.
I was thinking about this the other day I wish I used silicone on mine just for good measure. Water gets in every tiny gap conceivable.About to fit some OEM type bars from van style. Have to say I’m so glad I found this thread - the foam washer supplied with the fittings looks appalling and absolutely invites disaster.
And so I’m getting myself into a slight state of paralysis by analysis thinking this over. The instructions on this thread are pretty clear and I have the requisite parts on order, but I’m going belts and braces on this as I don’t want to regret fitting the bars.
A question for the forum sages…..
The op suggested he didn’t want to use silicon up the roof holes, but surely a small amount prior to the M6 bolt going in can only help create an absolute water tight seal, no? Also, a thin bead underneath the epdm washer and around the hole in the washer prior to the nylock nut tightening down? Any reason not to do either of the above that I’m not realising?
Thoughts?
About to fit some OEM type bars from van style. Have to say I’m so glad I found this thread - the foam washer supplied with the fittings looks appalling and absolutely invites disaster.
And so I’m getting myself into a slight state of paralysis by analysis thinking this over. The instructions on this thread are pretty clear and I have the requisite parts on order, but I’m going belts and braces on this as I don’t want to regret fitting the bars.
A question for the forum sages…..
The op suggested he didn’t want to use silicon up the roof holes, but surely a small amount prior to the M6 bolt going in can only help create an absolute water tight seal, no? Also, a thin bead underneath the epdm washer and around the hole in the washer prior to the nylock nut tightening down? Any reason not to do either of the above that I’m not realising?
Thoughts?

Have done with them and replace them with fixed windows. One of the best mods I've done to my van! However the list of mods is utterly endless but enjoyableI use that stuff at work . My only grip is that it can set hard on some makes so can be tougher to remove. But that’s what it is for and will still work. Main thing is you put something on to stop it leaking . Wish I could slap it on the kombi windows to stop them leaking!