Yes I believe it was at one point Brass but has gone dull with age, I've never had chance to take one of these sockets off but they look a lot like the light switched that where made by Crabtree.
Wish I could have got in before they closed the depot and rescued some of this gear.
I recall the holes were to allow test probes to see if the fuse was blown. My uncle had a couple of similar ones in his shed. Probably had to be 4 holes to ensure there was a hole over both terminals no matter where the cap stopped ( jammed ) while being tightened. I also recall one that had jammed and the cover had to be cracked in half to replace the fuse.
The hole in the biro was to allow the ink to leak out and ruin the shirt pocket.
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