An oil repellent layer is applied to {HEAD ~ either the surface portion} having {TAIL ~ grooves} thereon or its opposing surface in the vicinity of the narrower gap 
having
An oil repellent layer is applied to { HEAD ~ either the surface portion } having { TAIL ~ grooves } thereon or its opposing surface in the vicinity of the narrower gap
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH