US federal government, there are 2 sub sets for Optical Character Recognition : OCR-A and OCR-B.

ANSI INCITS 17-1981 (R2000), formerly known as ANSI X3.17-1981 (R2000), specifies the shapes and dimensions of OCRA.

ANSI X3.49-1975 (R1982) describes nominal shapes, sizes, and printing positions of OCR-B. Most part of OCRB is identical to what is defined by ECMA-11.

Both OCR-A and OCR-B character sets can be printed in three different sizes (I, III and IV) in order to provide for their use with a wide rane of printing devices. Eash size is differentiated by its unique scale factor and stroke width.

The choice of sizes for OCR-B application is basically based on requirements for the following printing device:
Size I is used for typewriters and printers.
Size III is used by cash registers and accounting machines.
Size IV is usded by credit card imprinters.

Barcodesoft OCR font package contains the following font files: OCRA I, OCRA III, OCRA IV, OCRB I, OCRB II and OCRB IV.