rivrduk, since you see rails with gear teeth under your slide-out, you have the rack and pinion-type, which is the type that has pins (actually bolts) that break.
Our slide-out mechanism is made by Power Gear, which is probably the most common make of electric slide-out mechanism. On longer slide-outs, there will be 4 bolts. There is an electric gear motor in the center with 2 square drive bars going to the rack and pinion mechanisms at each end of the slide. Each end of the 2 square bars has a connecting bolt, and it's these bolts that tend to shear.
The original bolts and nuts are special Grade 8 bolts with a longer than usual unthreaded shank on the bolt. The nuts are also special and have an unthreaded lip at the bottom edge.
Most people (myself included) replace a broken slide bolt with a standard Grade 8 bolt that you can buy in Lowe's or Home Depot. I always carry at least 3 or 4 spares. Look for the large sliding drawers in the hardware section that have the special fasteners. Grade 8 bolts have 6 radial lines on the head.
You can use a standard bolt to get by in a pinch, but a standard bolt really won't last long at all. I tried it once, and the standard bolt broke after only 1 or 2 more operations of the slide.
According to Power Gear, the reason the bolts keep breaking is because of the use of standard bolts and nuts instead of the special ones. The longer unthreaded section of the special bolts makes the part of the bolt that is in shear stronger.
Proper torque of the bolt is also important. The Power Gear instructions call for 15 lb-ft of torque. The Power Gear web site has torque instructions that you can read about HERE
. The instructions also give the part numbers and drawings of the special bolts and nuts.
I can change a bolt in about 3 minutes, but it's an inconvenience, so I am thinking about getting some of the special bolts and nuts to see if they last longer.