Here is a size chart for common couplers:
https://www.discounthydraulichose.com/v/vspfiles/downloadables/qd_sizechart.pdf
You probably have either 1/2" or 3/8" ag couplers
ag couplers have ball or poppet ends. The ag couplers in the diagram have ball ends, the series A couplers show poppets. While they're supposed to interchange they sometimes don't. It's best to get the same type so they match. Pioneer and Safeway are good brands.
While the couplers are usually NPT threaded, NPT threads suck for hydraulics. They have to be super tight, they leak uness sealed, and they dont' reuse well. JIC has none of those problems. I recommend using NPT to JIC male adaptors and then hoses with JIC female swivels. Use Loctite 545 sealant on the NPT threads.
Usually there are 4 females on the tractor size and 4 males going to the loader. Whatever is on the loader make sure you know which lines go where. Often there are four different colored dust caps. On the other end you'll need males and females. They make JIC bulkhead fittings so you can make a bracket instead of leaving them flopping around.
Surpluscenter and discount hydraulic hose are good places to buy fittings and hoses. I use old garden hose to mock up the hydraulic hose runs for sizing.
Put the loader bucket in a neutral position when you unplug it so there is less pressure on the hydraulics when you go to reconnect. If there's much pressure it makes connecting the fittings difficult.
1/2" ag couplers are the most common for the implement side. Pioneer 4200s are about $25 for a set as TSC. Those and Safeway S40s have two way sleeves on the female coupler which makes connecting and disconnecting easier.
