A magnetic gap in a solenoid core is formed by a non-magnetic brazing material bonded into a groove encircling the core in the region of the magnetic gap. A bore through a single piece core and valve cartridge is dimensioned to intersect the brazing material and remove magnetic material bridging the gap without severing the core into separate pieces. This allows the solenoid core and the valve cartridge to be machined in a single piece with a uniform diameter bore receiving a single piece solenoid plunger and valve spool. This ensures accurate concentricity of the plunger and spool within the bore, which improves magnetic performance while reducing manufacturing costs.