RAM A 9/16" Ball with Female Camera Thread Hole
The RAM-A-336U ball base, consists of a 9/16" diameter "A" size rubber ball, connected to base with a hole with female 1/4"-20 camera thread.

A black, 1/2" long pan head 1/4"-20 mounting screw and 2 lock washers are included.

Note: The mounting screw and lock washers are not provided by RAM.  They are provided by Cumulus Soaring, Inc.

Warning!
Most people find that the "A" sized components work fine for holding a Pocket PC in an aircraft or automobile.  However, I have received a significant number of complaints about the rubber balls detaching from the bases.  I therefore recommend the larger "B" sized arms for most soaring applications.  In fact, one customer temporarily lost control of his sailplane when his PDA cradle fell off the RAM A arm and jammed the control stick.  I have never heard of a RAM "B" size arm component failing.