These are very nice quality Knuckles, and fit decently. The screws provided are the ONLY Screws that will fit these however, so if you lose them you are in trouble.
Also, the bottom screw shaft is longer than the plastic Radioshack ones, and i do not need to put a screw into the bottom.
The top screw shaft fits, but the screw isn't big enough to keep it from falling off.
I used this with the GPM Front swing shaft, and had problems of it popping out of the cup on the right side. All i did was put a washer into the gap between the shaft and the bearing on the inside of the knuckle and it works fine now.
I do not know how much better GPM is, but this works fine for me after a few modifications to it. I mean, for a whole 3 dollars less i'd say its worth it.