No u can't get longer threads, so cut a larger hole in the inner skin to give access to the glands locking nut/ring, although not so easy of neat now as if that had been done when there was only the pilot hole.
how long would the thread need to be? i have used glands with up to 25mm of thread so they are available (RS components i think would do them, as would marine electrical suppliers), although the gap behind the outer skin may just bow inwards and leak when it was tightend as there would be no ''crush tube'' as such. use a ''carbide bur'' in a power drill or die grinder rather than filing it will be much easier and faster.
I did have a look on their website but I can't find a M12 gland with a long thread, anything over 10mm. You've just introduced me to a "Carbide bur" though - so i'll buy one of those, that should sort it. Thank you!
I got hold of some stuffing glands.
I drilled a hole at the rear, but it has 2 skins of body work with about a 10mm gap between them - the thread on the gland doesn't reach so i can't secure it.
Can you get stuffing glands with long threads? I had a look but can't seem to find any. Is there any other similar solutions?
Thanks,
Foz