expansion bellows

i found this item and i don't know what does it mean "• Expansion bellows nominal bore, six (6") over all length stainless steel corrugated flexible tube of ANSI 321 or equivalent having forty (40)-forty two (42) convolution per foot fitted each end with BSPT BS 21 mild steel fixed male connector. Movement + twenty five (+25) mm from center line with at last twenty thousand (20,000) cycles without any leakage or distortion." so please if any one know what does it mean help me Received on Thu Dec 06 04:28:00 2007