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Randy Roberson
Frequent User
Username: wascator

Post Number: 855
Registered: 05-2009
Posted on Saturday, 26 March, 2022 - 06:27:   Edit PostDelete PostView Post/Check IP

Hi, my switch is missing, along with the two fasteners. Anyone recall the fastener thread type/size? Looks smaller than 2BA.
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Robert J. Sprauer
Frequent User
Username: wraithman

Post Number: 766
Registered: 11-2017
Posted on Saturday, 26 March, 2022 - 08:57:   Edit PostDelete PostView Post/Check IP

The fasteners, machine screw and nut have a very small diameter. Your replacement screws have to fit thru the mounting holes of the microswitch and long enough to go thru the hinge support.
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Alan Dibley
Frequent User
Username: alsdibley

Post Number: 345
Registered: 10-2009
Posted on Saturday, 26 March, 2022 - 19:47:   Edit PostDelete PostView Post/Check IP

They look like 4BA to me - that is just by squinting at mine.

Alan D.
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Robert J. Sprauer
Frequent User
Username: wraithman

Post Number: 767
Registered: 11-2017
Posted on Saturday, 26 March, 2022 - 21:12:   Edit PostDelete PostView Post/Check IP

Bentley Heritage does show the switch but not the fasteners. There is also a spacer involved.

https://heritage.bentleymotors.com/en/catalogue/partCatalogue/8506?chassisNumber=SRD21285#search-by-categories
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Randy Roberson
Frequent User
Username: wascator

Post Number: 856
Registered: 05-2009
Posted on Friday, 01 April, 2022 - 02:08:   Edit PostDelete PostView Post/Check IP

Not a 4BA; must be a 6BA or 8BA; I'm trying to fit a modern, more durable limit/microswitch so I may need to make new holes anyway. I'll try a small c-clamp to find a position which will enable to switch work correctly and go from there.
Thanks everyone!
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Geoff Wootton
Grand Master
Username: dounraey

Post Number: 2309
Registered: 05-2012
Posted on Friday, 01 April, 2022 - 02:58:   Edit PostDelete PostView Post/Check IP

Hi Randy

I was unable to source the original switch, the Bulgin S621, so fitted a cabinet door switch instead.

https://www.amazon.com/dp/B07YTC8VYH?tag=ftb-seller-20&geniuslink=true

It's worked perfectly so far. I did have to extend the push rod slightly by gluing a short length of heat shrink to it. I guess I should have painted the heat shrink black to disguise it but with the air filter in place the switch is hidden anyway.

I recall the bolts were 6ba.

a

b

.

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Randy Roberson
Frequent User
Username: wascator

Post Number: 861
Registered: 05-2009
Posted on Tuesday, 19 April, 2022 - 05:50:   Edit PostDelete PostView Post/Check IP

My fasteners are not 6BA; in fact a 6BA will pass right through the threads.
I saw a doc showing them to be M3 x 3/4 inch, but with a washer and nut. Hummm. I can't thread an M3 into it either, so there!
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Brian Vogel
Grand Master
Username: guyslp

Post Number: 3283
Registered: 06-2009
Posted on Tuesday, 19 April, 2022 - 08:37:   Edit PostDelete PostView Post/Check IP

Randy,

Given who made these cars, and when, the probability that they're metric screws is quite small.

Since I have no way to determine what the actual size of those fasteners is, even though I have a choice of two cars that have them at the moment, I can't be of any real help here.

Brian
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David Gore
Moderator
Username: david_gore

Post Number: 4086
Registered: 04-2003
Posted on Tuesday, 19 April, 2022 - 10:09:   Edit PostDelete PostView Post/Check IP

Randy,

Can you provide the following details on one of the original fasteners:

Thread count: Per inch or in metric, either will do

External diameter of thread: Imperial or metric

Root diameter of thread if possible: Imperial or metric

I suspect the fastener is either a model engineer's BA or Whitworth thread.

https://www.fastenerdata.co.uk/whitworth

https://maccmodels.co.uk/ba-size-chart/

Either fasteners are usually available from model engineering specialist suppliers.

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Randy Roberson
Frequent User
Username: wascator

Post Number: 862
Registered: 05-2009
Posted on Tuesday, 19 April, 2022 - 10:20:   Edit PostDelete PostView Post/Check IP

I do not have the original fasteners; sorry.
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Randy Roberson
Frequent User
Username: wascator

Post Number: 866
Registered: 05-2009
Posted on Monday, 25 April, 2022 - 22:12:   Edit PostDelete PostView Post/Check IP

UPDATE: I have installed the new limit switch and it is working as desired. Turns out the fasteners are 6BA, but there is a nut on the other side and the mounting holes are not threaded as I first thought. Thanks for all the great assistance!
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Robert J. Sprauer
Frequent User
Username: wraithman

Post Number: 772
Registered: 11-2017
Posted on Monday, 25 April, 2022 - 22:35:   Edit PostDelete PostView Post/Check IP

I usually install a SPST toggle switch with Lucar terminals in series with the switch so when the bonnet is left open, it won't drain the battery if there is no battery cut off switch.

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