Mr. David Klopp, Director

Quality, Testing & Compliance

Freedman Seating Company

4545 W. Augusta Blvd.

Chicago, IL 60651


Dear Mr. Klopp:


This responds to your request for an interpretation concerning the attachment hardware requirements in Federal Motor Vehicle Safety Standard (FMVSS) No. 209, Seat belt assemblies.  You ask whether it is acceptable to use attachment hardware smaller than that specified in the standard if the seating system complies with the strength requirements of FMVSS No. 210, Seat belt assembly anchoragesAs we explain below, under FMVSS No. 209 it is acceptable to provide attachment hardware other than the 7/16-20 UNF-2A or 1/2-13 UNC-2A attachment bolts specified in the standard if it meets 209’s S4.3(c) strength requirements [FD(1] when tested under the demonstration procedures of FMVSS No. 209’s S5.2(c).[JP2]   The agency will not use the FMVSS No. 210 demonstration procedures in place of those of S5.2(c).




FMVSS No. 209 specifies a variety of requirements for seat belt assemblies, including S4.3(c), which specifies strength requirements for attachment hardware that must be met when tested to a procedure in S5.2(c).  [FD(3] Section S4.1(f) generally requires, among other things, that a seat belt assembly include all hardware necessary for installation in a motor vehicle.  However, S4.1(f) goes on to exempt certain seat belt assemblies from this requirement:


[S4.1](f) Attachment hardware.  *  *  *  However, seat belt assemblies designed for installation in motor vehicles equipped with seat belt assembly anchorages that do not require anchorage nuts, plates, or washers, need not have such hardware, but shall have 7/16-20 UNF-2A or 1/2-13 UNC-2A attachment bolts or equivalent metric hardware.[1]


            Your question concerns the meaning of the phrase “equivalent metric hardware.”  You ask whether it is acceptable to use smaller (3/8” or M10 diameter) attachment hardware if the seating system (seat belts anchored to the seat structure) complies with the strength requirements of FMVSS No. 210. 




After examining the history of S4.1(f) regarding the phrase in question, we conclude that “equivalent” is referring to the alternate bolts’ meeting the strength requirements of S4.3(c) of FMVSS No. 209.  When the initial FMVSS No. 209 was promulgated in 1967 it incorporated by reference existing seat belt requirements codified at 15 CFR § 9.[2]  Section 9 required 7/16-20 UNF-2A or 1/2-13 UNC-2A fasteners; there was no provision for equivalent hardware.  The “equivalency” language was added later to FMVSS No. 209:


S3. Requirements.  Seat belt assemblies shall meet the requirements of [15 CFR §9] using the attachment hardware specified in paragraph (f) of 15 CFR 9.3 or approved equivalent hardware.”[3] 


            NHTSA explained in the preamble to the final rule adding the equivalency language that the agency had “determined that other fasteners that meet or exceed the strength requirements of paragraph (c) of 15 CFR 9.5 may be suitable for use.  Therefore Standard No. 209 is being amended to provide for the use of an approved equivalent of equal or superior performance as an alternative to the fasteners specified.”[4]  The strength requirements in 15 CFR § 9.5(c) for attachment hardware were later re-codified at S4.3(c) of FMVSS No. 209.[5]  In sum, this history shows that the equivalency language was intended to allow the use of hardware other than 7/16-20 UNF-2A or 1/2-13 UNC-2A attachment bolts as long as the hardware meets or exceeds the strength requirements specified in S4.3(c).[6] 


            These S4.3(c) strength requirements remain the same today.  They specify that attachment hardware must withstand specified forces when subjected to the test procedures in S5.2(c) of FMVSS No. 209.  This test involves applying a load to the bolt through attachment hardware from the seat belt assembly, or through a special fixture which simulates the loading applied by the attachment hardware. 


            Note that S4.1(f) and S4.3 do not contemplate an FMVSS No. 210 strength test to assess the equivalency of alternate hardware.  Thus, to answer your question, NHTSA will not assess compliance with S4.3(c)’s strength requirements using the FMVSS No. 210 demonstration procedures.

“Equivalent Metric Hardware”


We recognize that the agency’s intent to state in FMVSS No. 209 that a manufacturer may provide equivalent hardware was somewhat obscured by a subsequent amendment.  The “equivalent hardware” language remained until 1998, when the standard was amended as part of a rulemaking that converted English system measurements in selected FMVSSs to the metric system.[7]  Section S4.1(f) of FMVSS No. 209 was amended by changing the phrase “equivalent hardware” to “equivalent metric hardware.”[8]  It was not the intent of the 1998 metric conversion rulemaking to make a substantive change to FMVSS No. 209.[9]  Instead, the intent was that “equivalent hardware” was still the rule.  Therefore, the agency interprets the S4.1(f) requirements to permit, as they have since 1967, fasteners other than 7/16-20 UNF-2A or 1/2-13 UNC-2A that meet or exceed the strength requirements in S4.3(c) when tested according to S5.2(c). 


If you have any further questions, please contact John Piazza of my staff at (202) 366-2992.






                                                                        Jonathan C. Morrison

                                                                        Chief Counsel



Dated: 8/12/19

FMVSS No. 209

[1] (Emphasis and footnote added.)

[2] 32 FR 2408 (Feb. 3, 1967).

[3] 32 FR 3390-91 (Mar. 1, 1967) (emphasis and footnote added).

[4] Id. (emphasis added).

[5] 34 FR 115, 117 (Jan. 4, 1969) (recodification).  Also, NHTSA amended FMVSS No. 209 to remove the word “approved” from “approved equivalent hardware.” 

[6] See also NHTSA’s letter to Takata Kojyo Co, Ltd. (Apr. 9, 1973) (stating that “[u]nder the provisions of S4.1(f), ‘equivalent hardware’ is permissible in lieu of the 7/16" bolts.  In such a case, the tests required under S4.3(c), as prescribed under S5.2(c), would be performed on the entire equivalent hardware, rather than or the individual components (bolts).”).

[7] 62 FR 19253 (Apr. 21, 1997).

[8] 63 FR 28922, 28936 (May 27, 1998) (final rule).  See also letter from Paul Jackson Rice, Chief Counsel, to J.W. Lawrence, Volvo GM Heavy Truck Corporation (May 8, 1992) (stating that equivalent metric hardware is permitted).

[9] 63 FR 28922 (“The [metric] conversions are not intended to make any changes in the stringency of the affected FMVSS”).

 [FD(1]Just asking--what about the other 209 requirements for hardware?


JP: Yes, I agree--see my comment above—these attachment bolts are just one type of hardware, and there are requirements for those other types  of hardware.  The interpretation request, and this letter, are only about the requirements for attachment bolts in S4.1(f).

 [JP2]I don’t think this is totally correct as  written.  “Hardware” refers to more than just these bolts (for example, it also refers to anchorage nuts and plates, S4.1(f), and buckles, S4.3), but this sentence makes it sound like this condition applies to all hardware.  I tweaked it a bit to make this clearer.

 [FD(3]I added this because I was concerned that S4.1(f) is silent about strength.  You rightfully discern a strength requirement from the reg history but I wanted to have something more in the reg text to stand on.