Hollow Square Mortise Chisel

Size: 5/16 inch
[7,9mm]
Most mortisers are equipped to handle 1/4′, 3/8′, 1/2′ and 5/8 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