Always best to try 1st if you have any doubts
On the strap...All my DW6900's have two grooves the only time I ever saw 3 was when folks swap the band for what I think is a DW5800 band?
Someone can chime in on that
That yellow H9 I just posted is over 18 years old now receipt is dated 3/28/97 But all my DW69's have the 2 groove strap
PS: see below? I'm not a bear heheh