RAM® Composite Ball Adapter with Round Plate and 1/4"-20 Threaded Stud
Base Plate, Round, Plastic, with 1" (25.4 mm) "B" Size Ball, with Male 1/4''-20 thread

2 7/16" (62 mm) diameter plastic base plate with Male 1/4''-20 thread.  This is the similar to a RAP-B-202U with a Male 1/4''-20 thread.  The 1/4" thread could be used to hold a camera or GPS/logger such as a Cambridge GPS-NAV (but not a Volkslogger which has an M5 thread).  For that application you would also want a RAP-B-201U arm and a RAM-B-224U suction cup (for canopy mounting) or RAM-B-238U base (for instrument panel or cockpit sidewall mounting).

SPECS:

Hole Pattern:
4-Hole AMPS: 1.181" x 1.496"

Ball Size:
B Size (1")

Weight Capacity:
Standard Use: 2 lbs
Heavy-Duty Use: 1 lb

Materials: 
High strength composite

Weight:
0.12 lb

Q&A
Q: What is the usable length of the threaded stud?
A: Just slightly under 1/2".