[rollei_list] Re: ?? True Sizes of Tripod Mounting Holes
----- Original Message ----- From: "Frank Dernie" <Frank.Dernie@xxxxxxxxxxxxxx> 
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Tuesday, August 28, 2007 2:51 AM
Subject: [rollei_list] Re: ?? True Sizes of Tripod Mounting Holes
This doesn't help but I thought the two standards were both Whitworth 
thread form not UNC.
Frank

On 28 Aug, 2007, at 03:14, Laurence Cuffe wrote:
On Monday, August 27, 2007, at 07:50PM, "SandyF." <sbf70@xxxxxxxx> wrote:
According to the Unified Standards, the following applies to UN Coarse Series Threads 

Size      Basic      Threads/inch   Basic
           Major                            Pitch
           Dia. (in)                        Dia. (in)
1/4-20   0.2500           20          0.2175
3/8-16   0.3750           16          0.3344
The above information straight from my Machinery's Handbook, 21st ed. 
S. B. Friedman, aka
SandyF  -----  Ö¿Ö¬


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I found a thread standard in a reprint of a book I think originally printed by the National Camera School. For American cameras the thread was covered by ASA standard PH 3.6-1952 This specifies a 1/4-20 UNC-1A thread according to Unified American Screw Threads B1.1-1949. The standard is slightly different than the one given above by Sandy.
Major Diameter (inches) Pitch Diameter (inches) Minor Diameter (inches 
Max   0.2489            0.2164                  0.1876
Min   0.2367            0.2108                  ------
Recommended length: Small cameras = 0.175"; Large cameras, 0.340"
The standard also has a recommendation for an oversize thread to account for build up during plating. 

   Screw Socket Dimensions: 1/4-20 UNC-1B
Minor Diameter (inches) Pitch Diameter (inches) Major Diameter (inches) 
Min    0.1959            0.2175                   0.2500
Max    0.2067            0.2248                   ------
A second ASA standard, ASA PH3.7-1952, applies to heavy duty cameras and European cameras. The thread specified is: 3/8-Inch-16 UNC-1A American Unified Screw Threads ASA B1.1-1949 with the following dimensions:
Major Diameter (inches Pitch Diameter (inches) Minor Diameter (inches 
Max  0.3737             0.3331                  0.2970
Min  0.3595             0.3266                  ------
Screw Socket Dimensions: 3/8-inch 16 UNC-1B according to PH B1.1-1949
Minor Diameter (inches) Pitch Diameter (inches) Major Diameter (inches 
Min   0.9373             0.3344                   0.3750
Max   0.3182             0.3429                   ------
This standard also gives recommended dimensions for a thread adaptor to the American size thread. 

------------------
I hope this survives word wrapping.

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx

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