Through holes are formed when {HEAD ~ the beam} penetrates through {TAIL ~ the entire thickness t} of the substrate 18 
Through holes are formed when { HEAD ~ the beam } penetrates through { TAIL ~ the entire thickness t } of the substrate 18
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH