Hello, when I put a new outer 50t chain ring on my bike one the the bolts came out (stiff) unlike the others. When I put the new ring on all the other bolts took well. I put some grease on the final one and when I tightened them all up, I found that the dodgy one has I think stripped (it suddenly moves with little force. So my question is - is there a tool (or technique) to remove the (starry shaped) cup that the bolt sits in (see picture). This would enable me to take out the bad stripped cup and put another one in. Many thanks.