It is also specific to the subset of machines with 13" throat depth (that's the measurement needle to throat). Did you see the note in the item?:
"*Note: This table was designed for large machines with free arms longer than 13”. If your free arm is shorter than this, this size of table may not be ideal as the needle will be more than 10” from the front of the table."
Oh shucks- The 770 is 10” to needle. 13” arm length. Did I read it wrong?
*Note: This table was designed for large machines with free arms longer than 13”. If your free arm is shorter than this, this size of table may not be ideal as the needle will be more than 10” from the front of the table.