Question about column u joints

I need to get my some 3/4" joints for my steerin column for my Luv. My question is on flaming river's website I'm confused about the description. There are two different 3/4" joints w/a number behind them: 3/4" smooth X 3/4-30, 3/4" smooth X 3/4-36. What does the (30 and 36) stand for? Thanks for the help!

I think I figured it out, pretty sure its spline size....

or spline count. junkyard them. 87-96 2wd dakotas have two on the shaft. as do almost any FWD cars. those, because the rack is behind the front wheel centerline so it has to turn straight down out of the firewall. VWs have multiple i think.