The attached photo shows the stud/pin people are talking about. It is the thing that goes into the hole in the ball on the socket yoke. It should be exactly 0.500" in diameter. In my opinion, measuring it is not as critical as visually examining it. When they are worn they will typically be visibly worn. This could be in the form of the following.
- Tapering. The pin should be perfectly cylindrical and not conical or tapered.
- Notching. The needle bearings of the socket yoke can wear grooves into the pin. This is usually visible but is also easy to feel with your fingers.
- Needle bearings in the socket yoke are dry, rusty, or ground to dust upon removal of the old socket yoke. Bad wear on the socket yoke / centering ball is what causes wear on the pin. If you catch the socket yoke early enough it is not likely to do damage to the pin.
- Heat discoloration. These things are shiny silver color when new. dark heat discoloration is usually a sign wear has taken place.
If it's anything other than a smooth looking and feeling shiny cylinder then it is time to get out the calipers and measure it.
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