After having another couple of the 'as fitted' bobbins failing , I decided to look for something a bit stronger and long lasting.
I have had these alternatives on now for over 1000 miles including some serious competitive events and no failures .... I have almost stopped checking for cracks in the rubber which is dangerous.
They look and feel sturdier due to the larger diameter, and as they dont reduce in size in the center.
http://www.ebay.co.uk/itm/281280225096?_trksid=p2060778.m1438.l2648&ssPageName=STRK%3AMEBIDX%3AIT
They are a bit bigger diameter than standard, and on one face only I needed to trim the bonded metal washer down on two sides with a quick lick with an angle grinder so it fits in the vee shape where it attaches to the body.
Bolt size is the same as normal.
