Robertson screws

[Model "A" Fords]

Originally Posted by johnneilson

No, the standard numerical sizes as follows;
starting with a "0" the major diameter is .060

add .013" for every number up

"2" is .060 + .026

"4" is .060 + .052

this from 7th grade machining class, I guess schools are missing out now...

J

As johnneilson says above:

To calculate a number screws diameter we use O.060" the constant for any number screw and 0.013" the constant for the individual screw number.

The formula looks like this: screw constant + ( screw number X the screw number constant )= outside diameter. Examples below.

#0= 0.060 + (0 x 0.013) = 0.060 + 0 = 0.060"diameter

#1 = 0.060 + (1 x 0.013) = 0.060 + 0.013 = 0.073" diameter

#2 + 0.060 + ( 2 x 0.013 ) = 0.060+ 0.026 = 0.086" diameter

#3 = 0.060 + ( 3 x 0.013 ) = 0.060 + 0.039 = 0.099" diameter

#4 = 0.060 + ( 4 x 0.013 ) = 0.060 + 0.052 = 0.112" diameter

#5 = 0.060 + ( 5 x 0.013 ) = 0.060 + 0.065 = 0.125" diameter

#6 = 0.060 + ( 6 x 0.013 ) = 0.060 + 0.078 = 0.138" diameter

#7 = 0.060 + ( 7 x 0.013 ) = 0.060 + 0.091 = 0.151" diameter

#8 = 0.060 + ( 8 x 0.013 ) = 0.060 + 0.104 = 0.164" diameter

#9 = 0.060 + ( 9 x 0.013 ) = 0.060 + 0.117 = 0.177" diameter

3/16 ( British standard, not a number screw ) = 0.1875" diameter

#10 = 0.060 + ( 10 x 0.013 ) = 0.060+ 0.130 = 0.190" diameter

#12 = 0.060 + ( 12 x 0.013 ) = 0.060 x 0.156 = 0.216" diameter

#14 = 0.060 + ( 14 x 0.013 ) = 0.060 x 0.182 = 0.242" diameter

To sort out the #10 ( 0.190 diameter ) and 3/16" screw (0.1875" diameter ), these are not the same, as is shown below. A 0.190" diameter pin does not go into 0.1875" diameter hole

They are sometimes thought to be the same, because if a #10 screw is made sloppy/undersized it may fit in the 3/16" tapped hole. Likewise the 3/16" screw is a smaller diameter and may thread into a #10 tapped hole, but may be a sloppy fitt.

If the two sizes were set to extreme tolerances. Say #10 screw on the low end tolerance and the 3/16" tap on the high end tolerance they may fit. If the tolerances are made extreme opposite they won't fit because they would be an interference fit.

Just as a 5/16" and an 8mm bolt are different, the #10 and 3/16" are just close enough to "SCREW THINGS UP "