Garage Door Rollers Nylon vs Steel - Nylon and steel are the two most common garage door rollers. The nylon garage door roller is going to be quieter and smoother operating than the steel garage door roller. The nylon rollers won't rust and will last longer than the steel rollers. The only downside to a nylon roller is that they cost a little more than steel rollers and the wheel of the roller can quickly wear out if the connection between the horizontal and vertical track (where the curved piece of track meets the vertical track) is not smooth. Check and make sure your track is aligned properly and you shouldn't have any problems.
Short Stem or Long Stem Roller - The short stem roller is what you will find in most residential garage doors. The typical working length of the roller stem will be approx. 3-3/4" with the overall length around 4". A long stem roller will have a roller stem with a working length of 6-1/2" and an overall length of approx. 7". The long stem rollers can be used in the bottom corner brackets and top roller fixtures of a garage door when the garage door roller keeps coming out of the track. The spacing of the track may be off a little causing a roller to come out so a long stem roller will have more room to move and stay in the track. The long stem rollers will also be typically found in larger commercial and industrial garage doors.
Cycle Rating and Ball Bearings - Garage door rollers will have a cycle rating. The cycle is the number of times the door goes up and down so a roller with a 10,000 cycle rating means the roller should last around 10,000 cycles before it fails and should be replaced. So the higher the cycle rating the longer the roller should last. And the ball bearings refers to the number of ball bearings in a roller. Some rollers don't have any ball bearings. Those are the inexpensive rollers that will not last very long. Look for rollers with at least 7 ball bearings but 10 or 12 ball bearing rollers will be better, smoother and longer lasting.