The outer surface {HEAD ~ 44G} of the sidewall 44C adjacent and above the air inlets 54 is provided with {TAIL ~ concentric ribs 44H.} In the preferred embodiment, there are two ribs 44H 
is provided with
The outer surface { HEAD ~ 44 G } of the sidewall 44C adjacent and above the air inlets 54 is provided with { TAIL ~ concentric ribs 44H. } In the preferred embodiment , there are two ribs 44H
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH