I have purchased a number of 57' suburban coaches, a mix of ex-LMS and Collett. All coaches come with a couple of alternative couplers which I like. However the Collett coaches R4878A, R4879A, R4880A, R4881 & R4881A all come with a couple of flexible grey strips in the same plastic bag as the alternative couplers. Can anyone shed any light on these, please