Stellar labs pm's you with a list of links after you purchase it, but these 3/16 barbs are the ones you need to split to the pressure gauge, and you need a Male barb fitting.
I'm honestly not sure on the size for the male barb, but it looks something like this. I went to my local hardware store with my pressure gauge and asked for help at their help desk and eventually found the thread size that fit, but I can't recall what size it is.
There isn't much information on the website regarding the wire and female connector they used. I'll see if I can measure my male barb later tonight to help!
Also, make sure you use some small hose clamps for that tighter seal! But those three items should be all you need. Stellar labs pm's you with a guide as well; but if you need it lmk, I'll pm you, it includes some pictures!
ps - make sure you get the 3/16 Tee splitter; I got the wrong sized ones at first and had to re-order lol