Preferably, the thickness of the resilient material is greater in {TAIL ~ a longitudinally center portion} than in the remaining portions of {HEAD ~ the bellows} and the distance between neighboring ridges in the central portion is greater than in the remaining portions 
Preferably , the thickness of the resilient material is greater in { TAIL ~ a longitudinally center portion } than in the remaining portions of { HEAD ~ the bellows } and the distance between neighboring ridges in the central portion is greater than in the remaining portions
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH