For fast transitions from tripod to shoulder rig, use this 2006 Drop-In Baseplate from SmallRig which is compatible with a separately available Manfrotto 501PL or 504PL quick release plate. The quick release plate drops, rather than slides, into the baseplate for fast mounting and unmounting.
The sturdy aluminum baseplate features two M3 safety screws to prevent the 501PL or 504PL plate from sliding out, and it tightens with a locking lever that secures with its own quick release buckle. There are multiple 1/4"-20 and 3/8"-16 threaded holes around the plate for mounting options. The 1/4"-20 threads on the front and back of the plates allow for mounting rail clamps or other accessories. Two Allen wrenches are included for adjusting the safety screws.