The C-30 clamp was made specifically for the old-style Wimberley Head (WH-100 & WH-101).
The added length of the C-30 (1.6" longer than the C-12) provides little added functionality for most applications. We recommend using the lighter and less expensive C-12 clamp.
We are still manufacturing the C-30 for use with an old-style Wimberley Head or in special applications that require a longer clamp.