Size: 3/8 inch [9,5mm]

Most mortisers are equipped to handle 1/4', 3/8', 1/2' and 5/8ƒ?? square chisels.
Converted to metric: 6,35mm, 9,5mm, 12,7mm and 15,9mm.

Some are even capable of handling a 3/4' chisel, but keep in mind that this is a pretty healthy chunk to cut at one time and may require a lot of physical exertion. Remember that even if you're cutting a mortise that is 3/4' wide, you don't need to cut the entire width in one pass. A few cuts down one side of the mortise and then back up the other with a 1/2' chisel will be just as effective and not nearly as taxing on you as the operator.

Advantages:

• Faster than a chisel by hand
• Consistent in size
• Strong joints
• Reliable joints
• Looks good
• Large glue surfaces enhancing the strength
• Convenient