According to some of the dusty tomes on my shelf, the strops used on Ark in the 70s were of two types, a standard one used by the Buccaneers and the Gannets which cost £5 each (in early 70s prices, when the average wage was between £30 and £50 per week pre the oil crisis) whilst te F-4s used strengthened ones that cost around £15 each. The need for the catcher is easy to understand.