My mortise gauge attachment easily fits into the body of my Rob Cosman Marking Gauge,  my "Cosmanized" Woodriver Marking Gauge, and most other marking gauges that use a 5/16 inch diameter rod.  

• Designed for marking out a mortise & tenon joint in furniture making.

• Width range between the two cutters: 3/16 inch to 11/16 inch wide.

• Works best for marking out cuts between 1/4 inch to 5/8 inch wide.

• Designed primarily for marking out the tenons but works for the mortises as well.

• Place your mortise chisel between the cutters, snug up the cutters to the chisel sides, using the knurled handle lock the cutters in place, remove the chisel.  Now your gauge perfectly matches the width of your chisel.

• When laying out tenons, the bevel / waste side of the gauge is perfectly located on the "waste" side of the line.

• When laying out mortises, the bevel / waste side of the cutter is located on the "keep" side of the line.

• Rob recommends laying out the mortise using just one line with a standard marking gauge, instead of this gauge.  The reason for this is it is much easier to register your mortise chisel to one line verses two lines when chopping.  

• A brass knurled locking handle

• An O-1 hardened cutter.