DESC: Oversized, bright-drawn profiled rail features I-beam design, minimizes flexing and bending common with flat bar clamps. Bright zinc rail finish prevents black marks on wood and won t ever rust. Unique, no-slip locking device with a set screw that is permanently molded into sliding arm to prevent slippage. The tighter you clamp, the tighter it holds. High-quality jaws are malleable cast-iron, precision fit to rail. Oversized, nonmarring pads protect your work, stops dimpling. Oversized Acme thread for positive-grip with minimum turns. Ergonomically designed wooden handle, comfortable fit allows maximum clamping pressure. Medium-duty, rail size: 1 x 5/16 and 880 lb. of clamping pressure. 4 throat depth and 8 opening.