Anyone know the diameter of pins on a 3MM LED?

I think it varies. Some I've used don't even fit into breadboards (usually 5mm) and some just fall out. Your best bet is probably measuring. How so if I may ask?

@ScriptCoded I'm trying to work out what size shrink tubing to get for around the pins.

I'm building a set of earrings inspired by these https://instructables.com/Simple-LE... for my definitely not a girlfriend for her birthday

might be easier to get a small set of various tubes 0.5, 1.0 and 1.5mm mix. they're usually pretty cheap

@TheBeardedOne Aaah! In that case I'd go with either 0.5mm or 1mm as @ojt-rant said (even though he's a PHP'er). 0.5mm should work, and even if it's too small you should be able to push them on. If you're worried it won't work go for 1mm and you'll be good as long as you actually heat them :)

@ScriptCoded PHBurn :)

Don't you have a datasheet for the LEDs you are using?

If you want to use heat-shrink tubes over pins soldered directly to wires, consider the diameter of the solder joints.