Longert coil sleeve (2.1875", 2 3/16" or 55.6mm).
If your coil is a bit lethargic, rather than replacing the whole unit, replace the coil sleeve. This particular item is for A-series coil bobbins. It will not fit a flipper coil.
Some older machines use steel coil sleeves. You may not be able to remove the sleeve from the coil and will have no choice but to replace the sleeve and the coil.