You need to get the bit out before you screw in a new one. The end bit forms a seat inside the bleed hole, as you undo it it allows air/fluid to pass through the hole in the bleed nipple when you bleed the system. If you can't get it out then the end sits in the seat and blocks up the hole - no nipple, no bleedy[xx(]
Summer's here.....
Told you
Summer's here.....
Told you