[Healeys] Door Hinge center bolt

[Curtis Arndt]

William, David and Michael,

These hex screws (at least the one shown on the hinge in the photo) is/are
UNF and *NOT BSF*!

The "B" is the strength rating code and equates to a mild steel screw
equivalent to a US Grade 2.

What denotes a UNF versus a BSF screw is the circular dimple/depression on
the head.  This is outlined in the Austin Service Journal, the Concours
Guidelines, and in the Anderson Moment book section on fasteners (which
BTW, I helped to write).

See the attached documents and the section from my 1957 Machinery's
Handbook on how Unified fasteners (UNC/UNF) are distinguished from
Whitworth (BSW/BSF) fasteners .  The circular depression means it's a
Unified fastener (in this case, a hex head screw).

Cheers,

Curt

On Wed, Jul 22, 2020 at 8:21 AM WILLIAM B LAWRENCE via Healeys <
healeys at autox.team.net> wrote:

> I never noticed the holes were threaded. I just used them to position the
> threaded plate while attempting to start the hinge screws. Maybe they were
> used for that and the extra screw removed after the hinge was in place.
> ------------------------------
> *From:* Healeys <healeys-bounces at autox.team.net> on behalf of Michael
> Salter via Healeys <healeys at autox.team.net>
> *Sent:* Wednesday, July 22, 2020 12:58 PM
> *To:* healeys at autox.team.net <healeys at autox.team.net>
> *Subject:* [Healeys] Door Hinge center bolt
>
> The earliest 100s have "flat" hinges. In addition to the 4 countersink
> screws securing the hinges to the door post there is a single hex head
> 5/16" UNF screw in the center of the hinge plate.
> These screws can cause problems after they are installed because they can
> prevent the hinges from closing completely and can cause distortion of the
> hinge mount(s).
> I'm completely at a loss to understand a purpose for these screws ... does
> anyone have any idea why they are there?
>
> Thanks,
>
> M
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