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