Second this. Obviously, they have to match the tractor. I changed all mine out to 1/2" flat face, but 3/8 would be big enough for OP. I like that you just pull the collar back to disconnect, then the collar stays cocked. So when you push the two parts together, the collar locks without having to hold the collar back while pushing the two parts together.I recently did a DIY 3rd function and added a grapple for my little LX3310. I went with 3/8" flat face fittings and the more I use them the more I like them. When I take all the pressure off to disconnect I just plug the two grapple fittings together. It seems every time I remove and install it the fittings get easier to connect and virtually no fluid loss when doing it.
1/4" flat face are less common but sufficient for a grapple. I mainly went with 3/8" because I wanted maximum flow to operate a mower I adapted.
^^^^You should match the same fittings on the front of the tractor for the third function.
I will add if it were me I would order the grapple with 3/8" flat face fittings and if those didn't match my third function I would change the third function fittings to match. Just saying.^^^^
That is the only correct answer based on the info provided by @STEVESC