metic thread

[yip]

 need to know what size thread for the screw that holds the cock to the thumber on a Pedersoli Pennsylvania  rifle, we know it's metic any help out there?

[Bob Roller]

Send a DECIMAL diameter and one of us on this forum will give you an answer.
Example: 2.75MM=.108 or American 4x40 or 4x48.

Bob Roller

[Scota4570]

https://custompartnet.com/tap-size-chart

I attached this chart to the wall in the shop, I use it often. 

Measure the OD of the screw with your caliper.
Measure the thread pitch with a thread pitch gauge.

Compare these to the chart above.

[Bob Roller]

https://custompartnet.com/tap-size-chart

I attached this chart to the wall in the shop, I use it often. 

Measure the OD of the screw with your caliper.
Measure the thread pitch with a thread pitch gauge.

Compare these to the chart above.

This assumes the owner has a metric thread pitch gauge.I am not
sure I have one among a comprehensive group of tools.
Without the guage the only thing that can be done is to measure the OD
with a micrometer or an accurate caliper.

Bob Roller

[Scota4570]

No need for a metric thread pitch gauge, I don't own one either.  The thread pitches are in TPI.  It will say, " ~32" for instance, when it is in between.  I have never had a thread I could not identify using this chart and the two tools specified.  It is pretty hand to have.

[ron w]

metric threads aren't registered as "threads per inch", they are registered as " the spacing in millimeters between threads major diameter. …… ie, "6mm X 1mm". or "5mmX .75mm".

[Ky-Flinter]

Ron W,

Did you look at the charts at the link provided by Scota4570?  They look pretty handy, and do include a "closest to" T.P.I. number for metric threads.  I can see how the charts could be used to ID a metric thread using a caliper and a standard thread pitch gauge.

-Ron

[Dale Halterman]

I believe he is try to determine thread size from the female thread in the tumbler shaft. A bit more problematic to find the pitch and an accurate diameter.

My local Ace Hardware has a good selection of metric nuts and bolts. You may be able to take your lock to a hardware store and find a machine screw that fits. They probable won't have the right head, but a least you will know the thread size and pitch.

Another thing I have done is whittle a hardwood peg that can be turned into the female thread. Once it is removed, you can measure the distance between the indentations made by the threads.

Dale H

[ron w]

Ky-flinter, no, I didn't look, I don't need to,...i'm pretty familiar with metric threads having worked with them all my career. I can jump back and forth between American, English and Metric threads quite easily.  spent my life working with Metric and American measurement on the same project or machine, converting back and forth all the time.