Hi SmokieDylan....first off the credit goes to MartyLeach here in the brethren who had it on his build and answered lots of our questions to help us out. THANK YOU MARTY!
I will try to give you what I know and maybe Marty can give you more info if needed.
We have a 1" solid rod that we made a 3/4 thread on for about 3.5" on the rod we then made washers that had a 1" ID and slipped that on first then we got a porch swing spring from home depot for a few dollars and cut that in half for each side, when then put another washer on there and then finally a 3/4 ID nut to hold everything in place. The more you you tighten it the more the spring compresses and the spring presses up against the washer where it meets the shaft that the rod goes into causing more or less friction to slow/stop the grates.
I have 2 grates on mine 1 of the grates weighs in around 68 lbs. the other about 40 lbs. We've noticed that the larger grate will need a larger spring due to the weight and the smaller grate could have probably worked with a 1/4 of the spring that it has now as it holds very well.
Hope this help!
Traeger Lil' Tex 075, Weber 22" and my newest...custom built Santa Maria grill!