Freight Car Reference Tools

About These Tools

Spring Calculator

AAR standard M-946 defines spring group codes for freight car truck bolster springs. Each group code specifies the load range, number of coil springs per bolster pocket, free height, and solid height required to meet the rated car capacity. The Spring Calculator on FreightParts.com accepts a car capacity in tons and optionally a car type (box car, hopper, gondola, flatcar, tank car, or coil car) and a truck type (100-ton, 70-ton, or 50-ton). It returns the spring group codes that match those parameters, together with the physical spring dimensions so a maintenance crew can confirm the correct replacement springs are on hand before beginning a truck swap. Selecting the wrong spring group -- even one with a similar free height -- can result in a car running at the wrong ride height, exceeding AAR interchange clearance limits, or failing a loaded car inspection.

Spring Groups Reference

The Spring Groups reference table lists every AAR-defined spring group code in a single sortable view. Each row shows the group code letter, the part type (inner or outer coil spring), the car capacity range the group is rated for, the applicable truck type, the number of springs in the bolster pocket, the nominal free height in inches, and the compressed solid height. Shops and procurement teams use this table when cross-referencing supplier catalogs against AAR group codes, when preparing bill-of-materials for a truck rebuild, or when auditing existing spring inventory for compliance with current AAR Interchange Rules. The table is sourced from AAR Field Manual Section IV specifications and is updated when AAR publishes revisions.

Identify a Part

The Identify a Part tool accepts an AAR part number, a manufacturer part number, or a free-text description and returns matching parts from the FreightParts catalog. Results include the part name, AAR classification code, manufacturer, applicable car and truck types, and links to the full part detail page where interchange equivalents and dimensional drawings are listed. This tool is useful when a shop receives a part with only a manufacturer stamp and needs to confirm the AAR interchange number for procurement, or when a maintenance engineer is cross-referencing multiple supplier catalogs to verify that substitutes meet the same AAR specification. Part numbers follow the AAR Manual of Standards and Recommended Practices (MSRP) Section C-II numbering scheme, which assigns unique identifiers to each component category and sub-type within that category.

AAR Standards Context

All three tools are grounded in AAR (Association of American Railroads) interchange standards. The AAR Interchange Rules govern which parts may be used in interchange service -- freight cars that operate across multiple railroads -- and prescribe specific dimensional, material, and performance requirements for each component class. The MSRP (Manual of Standards and Recommended Practices) provides the detailed engineering specifications that manufacturers must meet, and the Field Manual of the AAR Interchange Rules provides the maintenance and inspection procedures that shop personnel must follow. FreightParts.com draws on these documents to provide structured, searchable reference data for shops, procurement teams, and fleet managers working on AAR-interchangeable freight equipment.