National Model Railroad Association

• Join the NMRA
• About the NMRA
  • National Organization
  • Member Services
  • Publications
  • Online Store
• Education
  • Beginner's Guide
  • Achievement Program
  • Contests
• Resources
  • Standards and Conformance
  • Kalmbach Library
  • Howell Day Museum
  • Directory of Websites
  • Insurance
• Community
  • Conventions
  • Regions & Divisions
  • 100% NMRA Clubs
  • Special Interest Groups
  • NMRA Calendar

NMRA STANDARDS AND RECOMMENDED PRACTICES

• STANDARDS
  • 
  • S-1 General Overview - PDF
  • S-1.1 General Proto Scales - PDF
  •   S-1.1 - Draft submitted to BOD for Approval
  • S-1.2 General Standard Scales - PDF
  •   S-1.2 Draft submitted to BOD for Approval
  • S-1.3 General Hi-Rail Scales - PDF
  •   S-1.3 - Draft submitted to BOD for Approval
  • S-2 Couplers - PDF
  • S-3.1 Trackwork Proto Scales - PDF
    • -- Tech Note TN-1.1.2, Proto: Scale and Fine Scale revisions, 11/22/05 - PDF
  • S-3.2 Trackwork Standard Scales - PDF
  •   S-3.2 Draft submitted to BOD for Approval
  • S-3.3 Trackwork Hi-Rail Scales - PDF
  •   S-3.3 Draft submitted to BOD for Approval
  • S-4.1 Wheels Proto Scales - PDF
  • -- Tech Note TN-1.1.2, Proto: Scale and Fine Scale revisions, 11/22/05 - PDF
  • S-4.2 Wheels Standard Scales - PDF
  •   S-4.2 Draft submitted to BOD for Approval
  • S-4.3 Wheels Hi-Rail Scales - PDF
  •   S-4.3 Draft submitted to BOD for Approval
  • Note: For those using the 'new' HO code 88 (.088) wheels, see Fine Scale RP-3 and RP-4 below.
  • S-5 TRACTION Power Collection - (S-5 pdf)
  • S-6 TRACTION Clearance & Track Centers - (S-6 pdf)
  • S-7 CLEARANCES - (S-7 pdf)
  • S-8 TRACK CENTERS - (S-8 pdf)
  • S-9 ELECTRICAL - (S-9 pdf)
    • S-9.1 DCC Electrical Standard - (S-9.1 pdf)
    • 
    • S-9.2 DCC Communications Standard - (S-9.2 pdf)
  • Note: For Help with NMRA Gauge letter definitions and the AAR Plate diagrams
    on which it's based see: Standard S-7 Clearances and the NMRA Gauge
  • Note: For the Standards, the PDF is the definitive version. While the web page and the PDF should match, the PDF copy is the authority of the Standard.
• The RECOMMENDED PRACTICE category was established by the NMRA Board of Trustees in January 1957, to:
  • a. Promote maximum interchange between and within units.
  • b. Specify the details of major components to improve design and function.
• RECOMMENDED PRACTICES are only less mandatory than STANDARDS by virtue of their slightly less critical subject matter and/or the fact that deviation for specific reasons is permissible.
• RECOMMENDED PRACTICES
  • Recommended Practices Index (Printable Format) - (RP Index pdf)
  • 
  • RP-1 Abbreviations - (RP-1 pdf)
  • RP-2 NMRA STANDARDS Gauge - (RP-2 pdf)
  • Note: The NMRA does not sell a Standards gauge for S scale, (standard gauge). Modellers looking for an S scale gauge should contact the National Association of S Gaugers at:http://www.nasg.org. The NMRA does have the Sn3 gauge available.
  • RP-3 Fine Scale - Track - (RP-3 pdf) - Deleted.
  • RP-3.5 Hi-Rail - Track - (RP-3.5 pdf) - Deleted.
  • RP-4 Fine Scale - Wheels - (RP-4 pdf) - Deleted.
  • RP-4.5 Hi-Rail - Wheels - (RP-4.5 pdf) - Deleted.
  • RP-5 Electric Traction - General - with Proposals for Member Comment - (RP-5 pdf)
  • RP-5.1 Electric Traction - Trolley Wire Frogs - (RP-5.1 pdf)
  • RP-5.2 Electric Traction - Curvature & Drawbars - (RP-5.2 pdf)
  • RP-8 Three-Point Track Gauges - (RP-8 pdf)
  • RP-9 Electrical - (RP-9 pdf)
    • RP-9.1.1 Electrical Interface & Wire Color Code - (RP-9.1.1 pdf)
    • RP-9.1.2 DCC Power Station Interface - (RP-9.1.2 pdf)
    • RP-9.2.1 DCC Extended Packet Formats - (RP-9.2.1 pdf)
    • RP-9.2.2 DCC Configuration Variables - (RP-9.2.2 pdf)
    • RP-9.2.2 Appendix A DCC Manufacturer ID codes PDF Only - (RP-9.2.2 Appendix A.pdf)
    • RP-9.2.3 DCC Service Mode - (RP-9.2.3 pdf)
    • RP-9.2.4 DCC Fail Safe - (RP-9.2.4 pdf)
    • RP-9.3.1 Electrical Specifications for DCC Decoder Transmission - (RP-9.3.1 pdf)
    • Note: The red-lined RP below, dated July 2003, is considered OBSOLETE by the DCC Working Group. It should not be used to design or manufacturer new products. The draft RP posted below should be used for product design and will be used by the C&I Group for Conformance testing. Please be aware that this RP is in draft form and may be changed slightly by the Working Group. Please check with the Working Group before developing or manufacturing products that conform to this RP.
    • RP-9.3.2 DCC Basic Decoder Transmission - (RP-9.3.2 pdf)
    • RP-9.3.2 draft 2005-04-14.pdf
  • RP-10 Trackwork - General - (RP-10 pdf)
  • RP-11 Curvature and Rolling Stock - (RP-11 pdf)
  • 
  • RP-12 Turnouts - General - (RP-12 pdf)
  • RP-12.1 Turnout Dimensions - O Scale - (RP-12.1 pdf)
  • RP-12.2 Turnout Dimensions - S Scale - (RP-12.2 pdf)
  • RP-12.3 Turnout Dimensions - HO Scale - (RP-12.3 pdf)
  • RP 12.4 Turnout Dimensions - OO & On3 Scales
      -   (RP-12.4 pdf)
  • RP-12.5 Turnout Dimensions - TT Scale - (RP-12.5 pdf)
  • RP-12.6 Turnout Dimensions - HOn3 Scale - (RP-12.6 pdf)
  • RP-12.7 Turnout Dimensions - N Scale - (RP-12.7 pdf)
  • RP-13.5 Guard Rail & Frog Relationship - (RP-13.5 pdf)
  • RP-13.6 Guard Rails - (RP-13.6 pdf)
  • RP-13.7 Frog & Wing Rails - (RP-13.7 pdf)
  • RP-13.8 Flangeway Flares - (RP-13.8 pdf)
  • RP-15.1 Rail - (RP-15.1 pdf)
  • RP-20.1 Car Weight - (RP-20.1 pdf)
  • RP-21.1 Coupler Contour - (RP-21.1 pdf)
  • RP-21.2 Solid Couplers - (RP-21.2 pdf)
  • RP-22 Coupler Pocket - HO Scale - (RP-22 pdf)
  • RP-23 Bolsters - (RP-23 pdf)
  • RP-24 Trucks - (RP-24 pdf)
  • RP-24.1 Journals - (RP-24.1 pdf)
  • RP-24.2 Wheelsets - (RP-24.2 pdf)
  • RP-24.3 Axles - (RP-24.3 pdf)
  • RP-25 Wheel Contour - (RP-25 pdf)
  •   RP-25 Draft submitted to BOD for Approval
  • RP-37 Locomotive/Tender -Drawbar & Pin Relationship - (RP-37 pdf)
  • RP-37.1 Locomotive/Tender -Drawbar & Pin Dimensions - (RP-37-1pdf)

• ---

• MODULE STANDARDS
  • Introduction to Module Standards (Read for construction specifications) - (Intro pdf)
  • MS-1.0 . . STANDARD GAUGES - (MS-1.0 pdf)
  • 
  • MS-1.1 . . NARROW GAUGE - (MS-1.1 pdf)
  • MS-1.2 . . TRACTION/OVERHEAD STANDARDS - (MS-1.2 pdf)
  • MS-1.3 . . ELECTRICAL, ALL SCALES
    - (MS-1.3 pdf)
• MODULE RECOMMENDED PRACTICES
  • MRP-1.0 STANDARD GAUGES - (MRP-1.0 pdf)
  • MRP-1.1 NARROW GAUGE - (MRP-1.1 pdf)
  • MRP-1.2 TRACTION/OVERHEAD - (MRP-1.2 pdf)
  • MRP-1.2A TRACTION/OVERHEAD - (MRP-1.2a pdf)
  • MRP-1.3 ELECTRICAL, ALL SCALES - (MRP-1.3 pdf)
    
    • - Larger MRP-1.3 Drawing (Landscape) - (MRP-1.3b pdf)
    • See the note on the MRP 1-3 web page about the availability of Radio Shack 274-201 and Cinch P-302-CCTconnectors as shown in the electrical drawing.
  • MRP-1.4 TRANSITION MODULE, ALL SCALES - (MRP-1.4 pdf)

NMRA Standards & Conformance Department Email Contacts Page

These Standards and Recommended Practices are a publication of
THE NATIONAL MODEL RAILROAD ASSOCIATION, INC.
4121 Cromwell Road, Chattanooga, TN 37421
Permission to reproduce this copyrighted publication in whole or in part may be obtained upon written application to the Chattanooga office of the NMRA.

Copyright (c) 1995-2009 National Model Railroad Association. All Rights Reserved.
Last Updated: Friday June 19, 2009

National Model Railroad Association, Inc.
4121 Cromwell Rd., Chattanooga, TN 37421
Phone: (423) 892-2846 - Fax: (423) 899-4869
Email Contact List