[TR] TR3 bolt size?

[Dennis and Bridget]

Just verified on my 61 TR3A project:  The bolts that connect the plate to the frame are 3/8 x 24 (fine thread). The ones that came with my car (probably factory - they have the “correct” markings on the head) are 5/8” in length, though 3/4” length bolts would work just fine, and are probably easier to find locally.
Cheers, Dennis

> On Aug 29, 2025, at 3:10 PM, Allen Hess <allen.k.hess at gmail.com> wrote:
> 
> Hi Teri, First of all I have a 62 TR4, but I remember seeing a TR hardware catalog and I have found one on Triumph Experience. The nuts and bolts have part numbers and you will need a factory parts catalog to find those. 
> 
>> I would like to replace the bolts that connects the mount to the plate on the frame
>> 
> Aren't these studs integral to the trans rubber mount? If so I think it is a 7/16 fine thread nut
>> and possibly the bolts that connect the frame plate to the frame.
>> 
> these are ones that I can’t find but I would guess they are 3/8 fine thread and if not then 5/16. 3/4” length 
> 
> The big bolts trans to trans mount are #HB1112 1/2 x 1 1/2 fine, right side. #HB1115 is 1/2 x 1 7/8 left side when trans is fitted with the strap from bolt to gear shift.
> 
> Hopefully someone has a TR3 all apart and can give you a more definitive answer.
> <Triumph hardware sizes.pdf>
> 
>> 
>> From: "TeriAnn J. Wakeman" <tjwakeman at gmail.com>
>> Subject: [TR] TR3 bolt size?
>> Date: August 29, 2025 at 9:10:54 AM EDT
>> To: Triumph List <triumphs at autox.team.net>
>> 
>> 
>> My TR3 is currently my only functional vehicle and I need to replace the rear gearbox mount. Since the nearest hardware store is about 10 miles away I would like the swap to go quickly & smooth (yah right). I have a new mount & nuts that attach to the back of the gearbox. I would like to replace the bolts that connects the mount to the plate on the frame and possibly the bolts that connect the frame plate to the frame.
>> 
>> Could someone please let me know what size bolts are need to fit the gearbox mount to the steel frame bracket? And the size bolt  that connects the steel frame bracket to the frame? Since the TR is my only transportation I would like to quickly get in get the replacement done & get back on the road (as if any project goes as planned).
>> 
>> By the way, the U-joint part numbers I asked about earlier received a few replies all of which were obsolete numbers. Thank you to the people who took the time to reply and I suggest that you update your part numbers lists.
>> 
>> My TR's 20+ year old U-joints were badly worn but I discovered a broken rear gearbox mount. Hopefully to be sorted out soon.
>> 
>> My area's rainy season is due in the next month or so. It is getting to be time to remove the factory style luggage rack, polish it and place it into dry storage then get out the side curtains.
>> 
>> My baby doll
>> 
>> 
>> 
>> 
>> 
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