Abstract: A regulator for controlling and modulating the pressure of supplied gases includes an orifice, and a stem extending through the orifice. The regulator exhibits a flow capacity that depends, at least partially, on the relative dimensions of the orifice and the stem. The flow capacity of the regulator may be selectively changed via selective replacement of the stem with a stem of a different dimension. The regulator may include a mounting base, and a module coupled to the mounting base and that includes the orifice and the stem. The flow capacity of the modular regulator may be selectively changed, for example, by detaching the module from the mounting base, and either replacing the module with another module having an orifice of the same dimension and a stem of a different dimension, or by exchanging the stem with another stem of a different dimension while retaining the module.