This extreme duty replacement set of two snowblower shoes are designed to lift snow blowers up over sidewalk cracks up to almost 2 inches tall. Bottom runners are 12 in. long and are CNC laser cut from 1/4 in. thick steel plate, more than twice as thick as many stock skids. The leading edge of our skid is moved forward, to protect and gently lift snow blowers up over bumps. The angle of the leading edge is less than half that of most stock skids. For every bump the skid encounters, it has more than twice the distance to lift the snow blower up, compared to a stock skid shoe. Made with American steel. Gravel is brutal on snow blowers. Stock skids dig into gravel, leave ruts, and bend when they encounter frozen rocks. Armors skids provide a ski-like glide over uneven terrain, exactly what is needed for gravel driveways. This skid size has six slots: two slots spaced 2 3/4 in. apart on center, plus four more slightly offset slots spaced 2 3/4 in. apart to allow for offset mounting. Slots are designed to have a slightly loose fit on a 5/16 bolt. New bolts and washers not included. Note that due to size of skid there may be clearance issues with other bolts or protrusions on the snow blower. Either use large washers or SPC0300 spacer kit (sold separately) to space skid further outward if needed. Patent 8544856.