Thread sizes, plainly: ½ inch, ⅜ inch and the adapters between them

Bathroom plumbing in India is mostly standardised, and then, in any specific building, it is not. Knowing two numbers before you order removes most of the risk.

The two that matter

• Thread size. Commonly ½ inch for supply connections, with ⅜ inch appearing on angle stop valves and connector hoses. This is a nominal size — it does not equal the measurement across the threads with a ruler.
• Centre distance. For wall-mounted mixers, the distance between the two inlet centres. Get this wrong and the fitting will not reach, no matter how correct the thread is.

How to measure without a gauge

The reliable method is to take the existing part off and carry it to the counter — or photograph it beside a tape measure. Measuring an installed fitting in place is where errors creep in, because the visible part of a thread is shorter than the thread itself.

If the old fitting is unavailable, note the brand and model stamped on the body. Even when we do not stock that item, the specification is usually published and tells us what you need.

Adapters: useful, and not a cure-all

A ½ inch to ⅜ inch reducer solves a genuine mismatch and costs very little. What an adapter cannot fix is a centre-distance problem, a wall depth problem, or a thread standard from a different system entirely. Stacking two adapters to reach a fitting is a leak waiting to happen — at that point the right answer is the correct part.

Tape, not force

Thread tape seals; torque does not. Over-tightening a brass fitting to stop a weep is the most common way a perfectly good part gets cracked, and a cracked body is not a manufacturing defect. Two or three wraps of tape in the direction of the thread, hand-tight plus a quarter turn, is the usual answer.

Send us your two numbers before ordering and we will tell you plainly whether our part matches.