Sometimes the diameter is given in inches. So you can look for 0.015in 63/37 solder. I have been using the multicore solder below and have been happy with it.
This is the specific Kester solder that being referred to. 5.08mm is .020 in. Amazon product ASIN B00068IJWCIt's a whole pound of it, so it'll probably last you forever.
Edit: The forums replace amazon links with little cards that apparently uBlock origin, well, blocks. Turn off your adblock if you're not seeing the amazon listing.
This is the specific Kester solder that being referred to. 5.08mm is .020 in. Amazon product ASIN B00068IJWCIt's a whole pound of it, so it'll probably last you forever.
Edit: The forums replace amazon links with little cards that apparently uBlock origin, well, blocks. Turn off your adblock if you're not seeing the amazon listing.