The one I used when I built mine is a D03 hydraulic solenoid valve 4 way 3 position, P open to Tank with ports A & B blocked 12 VOLT DC
that I got from fremontindustrialsupply.com - the SKU then was: HD-3C6-G02-LW-F-DC12* but I looked that up and the number has changed.
Now to take a step back since you are (self admittedly) new to hydraulic terms.
There are two primary means of accomplishing a 3rd function for a grapple
Option 1
A Diverter valve - which uses a single momentary On/Off push button control along with an existing loader function (typical the bucket curl / dump function) to operate the grapple lid. Button off - the loader control stick works as normal, button on - the curl/dump motions now cause the grapple lid to open / close INSTEAD of curling/dumping.
PRO's - simpler to install, less cost (in general)
CON's - Cannot curl/dump grapple AND open/close at the same time. ** More on this later
Option 2 (Which sounds like what you're asking about)
A "3rd Function" solenoid valve - this set-up uses two momentary on/off buttons to control the open/close function of the grapple independently of the other functions **
PRO's - Allows independant operation of all three loader / grapple functions **
CON's - more costly and slightly more complex plumbing
** Now for the "fine print" - On most Sub Compact & Compact tractors the hydraulic systems has all of the various functions connected in series and the first function in the series to "ask" for flow will get it and little to none remains for the remaining functions down stream. The hydraulic system output (flow) on these models is not sufficient to operate multiple functions at the same time.
For a demonstration / test - raise your loader up, dump the bucket and then try to lower it & curl back at the same time. Generally speaking the loader will drop but the bucket won't curl back unless you're feathering things very gently.
So simply using a 3rd function solenoid does not mean you will be able to actually operate multiple functions at once. I opted to go ahead with the solenoid instead of a diverter because the way the controls function just feels more natural to me and plus between feathering the control and making several small adjustments at a time - I can get close enough to open/close and curl/dump movement at the same time.
Not trying to confuse you further, just want to make sure you are getting what you want for your money and it performs like you think it will.
I have attached the write-up I did of my 3rd function build. Different brand tractor - same basic concepts. Might give you a little more insight into what you're looking at.
Best of luck with your project. Don't be intimidated by it - there's plenty of help here to get you through it. Just take your time and plan it all out before you start.
Guess I need to do a little more research before I go crazy and spend a bunch of money. But I really appreciate all the help. Hope y'all have a good one and Happy Thanksgiving to everyone..JR