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