Help Identifying a Screw.

[Tbeltran]

This appears to be a fillister head, slotted screw, that is 1/2" X 20 the thread diameter is 0.310" which is on my Mastercraft Tools X-Y table.
Given the length, I measure approximately 5 threads per quarter inch. There is no shank from which to measure. It does not fit any nuts I have in my shop. I would like to replace it for a hex head screw. Thanks in advance for any assistance.

 

[kd4gij]

M8x1.25 possibly

 

[Tbeltran]

Thanks - I will try to find a metric nut and see.

 

[Video_man]

i think Kd4gij nailed it, this is from a program for cutting metric threads on an inch-graduated machine:

 

[darkzero]

Where is the tool made? Often that is a good indication if it's imperial or metric. I looked up Mastercraft & found it to be a Canadaian Tire brand of import tools. However I looked up Mastercraft X-Y Table & found it to be an old USA made tool. If it is chances are it may not be metric but still possible. Chinese made tools will most likely be metric & Taiwanese made tools can be imperial, whitworth, & metric.

Also try checking/measuring the female thread. I've ran into cases where the male threads on a scew of the female threads of a hole were made so out of spec that vise versa would seem to not match anything that was a standard spec yet fit or not fit.

 

[Tbeltran]

Where is the tool made? Often that is a good indication if it's imperial or metric. I looked up Mastercraft & found it to be a Canadaian Tire brand of import tools. However I looked up Mastercraft X-Y Table & found it to be an old USA made tool. If it is chances are it may not be metric but still possible. Chinese made tools will most likely be metric & Taiwanese made tools can be imperial, whitworth, & metric.

Also try checking/measuring the female thread. I've ran into cases where the male threads on a scew of the female threads of a hole were made so out of spec that vise versa would seem to not match anything that was a standard spec yet fit or not fit.

Thank you both, Video_man and darkzero - The attached, is the only thing I have been able to find.

 

[darkzero]

Yup, I highly doubt that to have metric hardware on it, gotta be imperial. I'm not sure how old it is but if it's old enough perhaps it could possibly have screw sizes that are uncommon today? I'm not too familiar with any of those sizes if that's the case.

 

[Tbeltran]

I wasn't thinking metric, only because of the age of the tool. But I plan on trying the screw in a nut to see. I bought this in the early 1980s, and it was old then. It is not cheaply made, but I doubt it was an expensive item either. I use it for wood working, and it works great, even on the drill press.

 

[Lo-Fi]

My money would be on 5/16 BSF.

Major diameter of 0.313, 22tpi. Zooming in, it looks like the Whitworth thread form too (rounded) , but it's really hard to tell from the photo. Other option is 5/16 UNF, which is also 313thou but 24tpi.

 

[Video_man]

An easy solution, M8-1.25 and 5/16-24 screws are common hardware store items, if you don't have them on hand already. Why not buy one of each and see which works? If none of the above, the uncommon (on this side of the pond) BSF that Lo-Fi mentions would be about all that's left.