From AP web page:
8" Dovetail Plate (DOVE08) - 400, 600E, 900
This versatile plate is suited for the 105 f6 Traveler and 130 refractors (we prefer the 15" Dovetail Plate for most applications of the 130 f8 StarFire EDT) and other short instruments. The knob assembly features a brass pin with a tapered end to hold your sliding bar firmly without marring the aluminum. Use with the SB0800 or SB1000 sliding bars, which are sold separately. Repositioning the sliding bar will aid in adjusting the balance of your instrument.
These are some of the uses:
Mounting cradle plate -
* 400 or 600E German equatorial mounts (all models) - attaches directly.
* 900 mount (all models) - Use part # Q4047 to attach this plate.
Used very little.
AP cost $85
My price $49 post paid.