Lotus Elan

SAE or Metric?

PostPost by: PDXjunkman » Thu Apr 14, 2011 5:29 am

Greetings,
I tried to find the answer in the archive but no luck. Can someone confirm the size of the fasteners used to hold the lens on the interior map light on my 1964 S1.
4-40 is two big .
Thanks so much.
Silas
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PostPost by: elansprint71 » Thu Apr 14, 2011 6:47 am

UK did not really adopt SI (Metric) units until 1974, the threads are therefore most likely British Association (BA) which were used for small screws and bolts, they are not designated by the outside diameter but by a numbering system 0BA, 1BA, 2BA, etc. If you can measure the O/D, someone over here with a Zeus chart can tell you the BA size you need.
I suppose there is even an extreme possibility that they might be British Standard Fine (BSF) but that is unlikely.

I'm am a UK Engineer and 4-40 means nothing to me, so I'm guessing that is a US only application.
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PostPost by: GrUmPyBoDgEr » Thu Apr 14, 2011 7:43 am

elansprint71 wrote:UK did not really adopt SI (Metric) units until 1974, the threads are therefore most likely British Association (BA) which were used for small screws and bolts, they are not designated by the outside diameter but by a numbering system 0BA, 1BA, 2BA, etc. If you can measure the O/D, someone over here with a Zeus chart can tell you the BA size you need.
I suppose there is even an extreme possibility that they might be British Standard Fine (BSF) but that is unlikely.

I'm am a UK Engineer and 4-40 means nothing to me, so I'm guessing that is a US only application.



I don't know the answer but agree that the thread will most likely be BA it being on a British electrical component.

Maybe you mean 4-48 Silas which would be a No.4 UNF designation?
I did a search but couldn't find a Unified 4-40
If you can measure the diameter of the thread we can probably be able to lead you in the right direction but availability where you are may still be a problem.
Cheers
John

Below a list of BA threads
1st Column BA Number from 25 BA (smallest) to 0 BA (largest
2nd Column Thread diameter in mm (1mm = 0,039370078")



Gage
Number Major
diameter
(mm) Threads
per inch
(approx) Pitch
(mm) Tap
drill
25 0.25 363 0.070 ?
24 0.29 317 0.080 ?
23 0.33 282 0.090 ?
22 0.37 254 0.098 ?
21 0.42 231 0.11 ?
20 0.48 212 0.12 80
19 0.54 181 0.14 78
18 0.62 169 0.15 76
17 0.70 149 0.17 75
16 0.79 134 0.1900 74
15 0.90 121 0.2100 72
14 1.0 110 0.2300 70
13 1.2 102 0.2500 65
12 1.3 90.7 0.2800 61
11 1.5 82.0 0.3100 56
10 1.7 72.6 0.3500 54
9 1.9 65.1 0.3900 53
8 2.2 59.1 0.4300 49
7 2.5 52.9 0.4800 46
6 2.8 47.9 0.5300 43
5 3.2 43.0 0.5900 37
4 3.6 38.5 0.6600 31
3 4.1 34.8 0.7300 29
2 4.7 31.4 0.8100 23
1 5.3 28.2 0.9000 17
0 6.0 25.4 1.0000 10
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PostPost by: bcmc33 » Thu Apr 14, 2011 9:23 am

4-40 is the smallest UNC thread size with a major diameter of 0.112" (2.84mm) so it is likely to be a BA thread that you need.
As 6BA has a major diameter of 0.1102" it is reasonable to suggest that the screws you need will be 7BA or less.
As a matter of interest, the size for the S4/Sprint rear lens is 6-32 UNC.
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PostPost by: GrUmPyBoDgEr » Thu Apr 14, 2011 9:54 am

bcmc33 wrote:4-40 is the smallest UNC thread size with a major diameter of 0.112" (2.84mm) so it is likely to be a BA thread that you need.
As 6BA has a major diameter of 0.1102" it is reasonable to suggest that the screws you need will be 7BA or less.
As a matter of interest, the size for the S4/Sprint rear lens is 6-32 UNC.



Ooops!
I didn't think about checking out UNC Brian.
If the other lenses etc are fixed with UNC Screws then probably the one in question should have the same type of thread.
My BA theory is most likely only relevant to much older cars :oops:
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PostPost by: bcmc33 » Thu Apr 14, 2011 4:37 pm

bcmc33 wrote:4-40 is the smallest UNC thread size with a major diameter of 0.112" (2.84mm) so it is likely to be a BA thread that you need.
As 6BA has a major diameter of 0.1102" it is reasonable to suggest that the screws you need will be 7BA or less.
As a matter of interest, the size for the S4/Sprint rear lens is 6-32 UNC.

I winced and shook my head having just read the above. :oops: :roll: :oops:
What I should have said is 7BA or smaller.
My English isn't what it should be.
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PostPost by: GrUmPyBoDgEr » Thu Apr 14, 2011 4:46 pm

bcmc33 wrote:
bcmc33 wrote:4-40 is the smallest UNC thread size with a major diameter of 0.112" (2.84mm) so it is likely to be a BA thread that you need.
As 6BA has a major diameter of 0.1102" it is reasonable to suggest that the screws you need will be 7BA or less.
As a matter of interest, the size for the S4/Sprint rear lens is 6-32 UNC.

I winced and shook my head having just read the above. :oops: :roll: :oops:
What I should have said is 7BA or smaller.
My English isn't what it should be.


Brian,

please join me in repeating:-

"Yes Sergeant I am a plonker" :lol:

Yup I think that English has become my 2nd language; time to get back home "'innit"
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