I'm working on a little project (a spotlight) that is basically a bit
of aluminium tubing, 50mm ID, 5mm wall thickness. I was wondering the
best way to close the end of the tube that doesn't have the light
shining out. I'm hoping to make it water resistant

a) Turn a round plate of 60mm diameter, drill and tap the tube and
screw the plate on - problem being the wall thickness isn't that great
so I'd be limited to about M3

b) Cut an internal thread in the tube and a threaded plug to fit
(probably a 1.5mm ISO thread) - would require some form of sealant/
threadlocker

c) Cut a chamfered plug and bond it to the tube - not sure what
adhesive to use

Any other ideas? I'll be using my Myford Super 7 and indexable tools