Lots of people get confused with this one and the Q1339A toner. The Q1339A toner only fits in the HP Laserjet 4300 series printers.
The Q1338A toner fits in the HP 4200, 4200n, 4200tn, 4200dtn, 4200tns and 4200tnsl printers.
Many HP toners also have a high capacity version, the Q1338A doesn’t as it already has a quite large yield of 12,000 pages.