An ignition coil includes a housing which contains a central core portion, an inner spool having a first winding, and an outer spool having a second winding. Methods of making the curable compositions and their use in the manufacture of abrasive articles are also disclosed. The piston sleeve extends around the piston, and is adapted for reciprocal movement therein. Sensing holes 56 pass into a hollow interior of the sensing structure 50 and pass on to a pressure sensor 60.