Here's the steps I took in grooving this tread.

Step 1. You can see the reference marks to assist in grooving. This cut was made using a 3/8'' blade set to 1/2'' wide by 5/8'' deep.
Step 2. This cut was made using a 3/8'' blade set to 9/16'' wide by 5/8'' deep.
Step 3. This cut was made using a 3/4" blade set to 7/8'' wide by 5/8'' deep.
Step 4 and final cut. This cut was made using a 3/8 blade set to 9/16 wide by 5/8 deep.