The Rack and Pinion Slides from Honeyville are in 8" to 24" flat square openings. Designed with a single rack in the center. Honeyville also offers a curved track for our U-Trough Augers that comes in 8" to 16" to match our Trough's. All Rack and Pinions have a 10-5/8" wheel set up for 3/16" coil proof chain.