Difficult drilling from the split end because the drill will bite/snag. If you take apart and drill from the back it would be better.
EDIT: not sure if the thread in the back would allow a big enough drill to pass through without damage, it's not something I've actually tried!
@dorsetbod My son's g/f's dad has started making leather goods, custom made by hand and doing guitar straps. If you would like to contact him, here's his facebook link;
https://www.facebook.com/sussexhandcraftedleather/
It's a very small - one man and his dog - operation and he's keen to get started, at very competitive prices!
Simple job especialy as you have the hole already, another socket wired in series with the original gives you the 2 outputs, two standard leads for split or one lead in either socket for normal.
Had a enquiry from Karl re a P loom, great comms, instant order and payment, perfect transaction followed up with super feedback.
The guy's a star!
Cheerz, John