{HEAD ~ a braking unit} adapted to apply {TAIL ~ frictional force} to the stopper, the braking unit having a frame defining a hole portion and a notch portion extending from the hole portion, the notch portion having a length longer than a diameter of the stopper, and a width of the notch portion gradually reduces as the notch portion extends away from the hole portion, 
{ HEAD ~ a braking unit } adapted to apply { TAIL ~ frictional force } to the stopper , the braking unit having a frame defining a hole portion and a notch portion extending from the hole portion , the notch portion having a length longer than a diameter of the stopper , and a width of the notch portion gradually reduces as the notch portion extends away from the hole portion ,
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH