Each notch comprises {HEAD ~ a first angled sidewall} and a second angled sidewall having {TAIL ~ an included angle} from horizontal 
Each notch comprises { HEAD ~ a first angled sidewall } and a second angled sidewall having { TAIL ~ an included angle } from horizontal
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH