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Tue Jan 31, 2006 2:25 pm

I just wanted to document the seatbelt bolts in my 68 Beetle for the benefit of anybody searching the archives in the same situation I was in: trying to purchase bolts to fit the existing threaded seatbelt studs.

For reasons unknown to me, these bolts are not metric; they're threaded SAE 7/16-20 -- that's a fine thread 7/16 inch bolt. All of the threaded seatbelt inserts are threaded this way: four behind the backseat, two on each door column, and two holding the seatbelt levers between the front seats.

VW may have used this fastener because of some sort of deal with Repa, the manufacturer of the OEM seatbelts during this time. Who knows; they just did it that way, in 1968 Beetles, and I'm sure several other models and years of Volkswagens around that same time period.

Here is a picture of an original door column bolt, alongside an original nylon washer that allows the seatbelt cleats some freedom to automatically adjust for the least slack.

You probably won't be able to find a shoulder bolt like this one at your local hardware store, but they usually carry a 7/16-20x1 inch bolt that's fully threaded, and you might get lucky and find a little 7/16 ID cylindrical piece to act as the shoulder part of the bolt.

Keywords: Repa seat belt lap belts seatbelt seatbelts bolt thread threaded threading size non-metric SAE screw fastener nut weldnut anchor shoulderbolt 2-point 3-point retractable harness

Sat Dec 16, 2017 9:34 am

thank you for noticing the lack of interest in original bolts very helpful I also know porsche used them also

Sat Dec 16, 2017 10:55 am

There was an agreement long ago from the manufactures to use this bolt I think it crosses over to metric.

Sat Dec 16, 2017 12:15 pm

pwmcguire wrote: There was an agreement long ago from the manufactures to use this bolt I think it crosses over to metric.

I used USF 7/16-20 when I installed retractable belts in my 1971; Internet search shows this to be the agreement size, like agreement on 14mm and 18mm spark plug threads, and 13, 14, 15 inch wheels even on our old beetles.

Some have claimed that an 11mm metric thread will fit; good luck finding those, you'll be older than our VWs by the time you try those.

Recommend USF 7/16-20, get from a seat belt company or elsewhere if you need ones with shoulders.

Sun Dec 17, 2017 1:30 am

Cusser wrote:
Some have claimed that an 11mm metric thread will fit; good luck finding those, you'll be older than our VWs by the time you try those.

11 mm x 1.25 thread.

It's easier just to go to the wreckers and pull seat belt bolts from any Japanese car, if you can't locate used VW.

Sun Dec 17, 2017 2:55 am

neil68 wrote:
11 mm x 1.25 thread. - It's easier just to go to the wreckers and pull seat belt bolts from any Japanese car, if you can't locate used VW.

X1, X2, X3

Yes you can get a 7/16" bolt to work, but it ISN'T THE RIGHT BOLT. Take a look at the very bottom of this thread, and I mathematically walk you through the difference.

https://www.thesamba.com/vw/forum/viewtopic.php?t=554235&highlight=

VW NEVER used an SAE thread anywhere on our cars.

Sun Dec 17, 2017 2:56 am

neil68 wrote: It's easier just to go to the wreckers and pull seat belt bolts from any Japanese car, if you can't locate used VW.

Absolutely agree! I bought the eBay Hummer seat belts and wasn't 100% satisfied with the fitment of the included bolts. I looked at every import car in the junkyard (with no impact damage, think about that) and took multiple seat belt bolts with several different lengths and shoulder dimensions. Y'all are right, a regular hardware store doesn't have the bolts we need to mount the seat belts up!

Mon Feb 10, 2020 8:30 am

For reasons unknown to me, these bolts are not metric; they're threaded SAE 7/16-20 -- that's a fine thread 7/16 inch bolt. All of the threaded seatbelt inserts are threaded this way: four behind the backseat, two on each door column, and two holding the seatbelt levers between the front seats.

This is true on my 72 super..I tried to size a bolt to get a new one and no metric would work. I found this thread and guess what he is correct...

Mon Feb 10, 2020 10:46 am

w.mainhotrods wrote: For reasons unknown to me, these bolts are not metric; they're threaded SAE 7/16-20 -- that's a fine thread 7/16 inch bolt. All of the threaded seatbelt inserts are threaded this way: four behind the backseat, two on each door column, and two holding the seatbelt levers between the front seats.

This is true on my 72 super..I tried to size a bolt to get a new one and no metric would work. I found this thread and guess what he is correct...
This topic of SAE threaded bolts in an otherwise metric vehicle caught my interest. I did a little research and found this copy of the Safety Standard 209 which was originally described the 1967/1968 US seat belt hardware requirement:
https://www.law.cornell.edu/cfr/text/49/571.209
Quote: (f) Attachment hardware. A seat belt assembly shall include all hardware necessary for installation in a motor vehicle in accordance with SAE Recommended Practice J800c (1973) (incorporated by reference, see § 571.5). 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...
I couldn't find an original 1968 version of the 209 standard. I'd be interested in seeing if the original version made allowances for metric fasteners?

As mentioned above, 11mm x 1.25 is nearly identical in diameter and thread pitch to 7/16"-20. So if a manufacturer were to use an "equivalent metric hardware" fastener to meet the US requirement they would choose 11mm even though it is a very uncommon metric size bolt. Sure they could have used a larger bolt (like the more common 12mm x1.25 which is closer to the 1/2" requirement), but that would cost more $$ in materials. VW wasn't averse to special threading as evidence by LH threaded fasteners in the front suspension.

Interestingly, VW was installing seat belt anchors into the early 60's Beetles. Someone mention having seat belt anchors in their '65 Beetle. These too were 7/16" or 11mm. It makes you wonder if the 1967 US standard was based on work already done in the auto industry, or if the US published a guideline before 1967 that VW proactively implemented?

Mon Feb 10, 2020 10:50 am

Good luck trying to find any 11mm bolts !

Mon Feb 10, 2020 3:50 pm

My understanding is that VW did use non-metric threads for seat belt mountings as that thread pitch a universally accepted standard for seat belts. Thread size is 7/16" UNF.

My '68 Euro beetle RHD Australian delivered beetle came with front seatbelts as law here in Australia. The bolts are definitely 7/16" UNF, not metric.

Mon Feb 10, 2020 3:55 pm

Here's an explanation from

https://www.thesamba.com/vw/forum/archive/index.php/o-t--t-631539--.html

Metric threads are allowed only if "equivalent" - IIRC, the US 'forced' all other countries ot follow this spec. due to market size, etc. I'm sure there is an ISO on it.

US Dept ofTransportation : Federal Motor Carrier Safety Administration
section 571.209

(S4.1)(f) Attachment hardware. A seat belt assembly shall include all hardware necessary for installation in a motor vehicle in accordance with Society of Automotive Engineers Recommended Practice J800c, “Motor Vehicle Seat Belt Installation,” November 1973. 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 1/2-13UNC-2A attachment bolts or equivalent metric hardware. The hardware shall be designed to prevent attachment bolts and other parts from becoming disengaged from the vehicle while in service. Reinforcing plates or washers furnished for universal floor, installations shall be of steel, free from burrs and sharp edges on the peripheral edges adjacent to the vehicle, at least 1.5 mm in thickness and at least 2580 mm 2 in projected area. The distance between any edge of the plate and the edge of the bolt hole shall be at least 15 mm. Any corner shall be rounded to a radius of not less than 6 mm or cut so that no corner angle is less than 135° and no side is less than 6 mm in length.

http://cfr.regstoday.com/49cfr571.aspx#49_CFR_571p209
and
https://law.resource.org/pub/us/cfr/ibr/005/sae.j800c.1973.pdf

Fri Feb 14, 2020 2:13 am

I thought this was a DEAD topic. Did anyone even click on my previous link where I mathematically showed the similarities and differences. My 92 year old dad opened the first VW / Porsche shop in the region (1958). In fact a ACVW has been my only form of a daily driver for my 42 years of driving, and VW never,ever, ever used a SAE thread for ANY application.

Fri Feb 14, 2020 1:06 pm

Multi69s wrote: I thought this was a DEAD topic. Did anyone even click on my previous link where I mathematically showed the similarities and differences. My 92 year old dad opened the first VW / Porsche shop in the region (1958). In fact a ACVW has been my only form of a daily driver for my 42 years of driving, and VW never,ever, ever used a SAE thread for ANY application.
Not interested in arguing that point, but I wonder if it is anything like pipe threads in Japan?? While I was living there I had to do some minor toilet plumbing work around the house... when I went looking for some plumbing fittings I was surprised they only came in odd metric sizes (sizes may be wrong as I’m pulling this from memory):
12.5mm = 1/2”
16mm = 5/8”
19mm = 3/4”
25mm = 1”
When I mated them with some spare US SAE NPT threaded fittings they matched perfectly. It was apparent to me that (for the things I was working on) the Japanese had just manufactured some SAE sized pipe fittings and labeled them their metric equivalents. In some cases the fitting had both a metric and SAE size stamped into them. This was the big give away. Technically, the parts were all metric sized.

So it makes me wonder if 11mm-1.25 is just a VW (or European manufacturing) way of using 7/16”-20 hardware in a metric production environment?? Obviously a “7/16 inch” part would be very confusing to German worker used to metric sizes, but an “11mm” part would not. If the difference in the measurements are within the allowable tolerance, are they essentially the same part with a different label?

Maybe I’m just over thinking this whole thing. If nothing else it is an interesting background story to our cars. :D

Sat Jul 18, 2020 2:23 pm

Very useful topic! Thank you for posting. We were struggling to get the correct size bolts for the threads on the spine between the seats.