What is the best way to correctly measure tub drain plug size?

Question

I have a tub drain plug I pulled out because part of it is missing, in order to replace it. However, I was under the mistaken assumption that there were only a few, distinct tub drain plug sizes. I'm having a hard time measuring it definitively. I pretty certain it's the 11.5 thread per inch variety, and then measuring the width of the threaded portion from thread extremity to thread extremity, I'm mostly getting 1 7/8 inch but sometimes get 1 3/4 inch.

How should I be measuring the plug size? Should I be using the threaded width, or should I use a different width? My measuring solution has been to take a level with a ruler on it, stick a card on the 0 inch side, push the drain against the card, and then use another card on the other side to take the measurement.

Answer 1

Know anyone with a set of calipers? Calipers

Or cut a match/toothpick untill it slots into the thread horizontally and can travel without binding or slipping off centre. That'll be her thread size(M30, M45, etc)

Just a thought...never tried it before. And if (by some miracle) works, set another match/toothpick parallel to it inside the thread and extrapolate threads per inch from the distance between the two.

Answer 2

Try taking a picture with a cell phone and nearby tape measure, perhaps also something like a quarter to add perspective. Then use tool such as photoshop to work out an approximate size. Then try to match to nearest 'standard size' available in hardware shop.