Comes with allen wrench for locking and unlocking. 
Dimensions:
5.5" across (outside) (13.97 cm)
3.75" across (inside) (9.52 cm)
17.5" around (outside) (44.45 cm)
14.25" around (inside) (36.19 cm)
1.25" o-ring opening (3.17 cm)
11.1 oz / 314.67 grams
 

Heavy-Duty Rolled Stainless Steel Locking Slave Collar with O-Ring

$51.95Price