There are fins/grooves on the head of the SC30 directly below where the open end of the clip contacts the head which I think can cause excessive wear when repeatedly clipped, and unclipped from the same location. The SC50 there is flat (non-finned/grooved) aluminum under the profile of the clip reducing the potential for wear. This can be seen if you look closely at the pictures located on the ZL website, and compare:
http://www.zebralight.com/SC50-Flashlight-AA-193Lm_p_24.html
Thanks Dh, that is a perfect illustration...nice work by zebralight to improve the clip design on the sc50. That confirms that I'd prefer the sc50 over the sc30.
SC30 clip pretty tight, but its shape allows you keep the flashlight is turned on/off/switch.
Thanks Misan.