Plumber needs a compression donut that fits a 3 1/8 inch cast iron coupling but the standard 3x2 donut is too large at 3 3/4 inches, and is seeking alternative options.

Standard donuts are sized for nominal pipe dimensions, but actual cast iron IDs vary, leaving a gap for odd sizes.

Severity

3Medium

Willingness to Pay

implied

Added

Apr 30, 2026

App Concept

FitDonut Custom Sizing

A web app that helps plumbers find the exact donut or adapter for non-standard pipe sizes by inputting actual measurements, with a database of odd-sized fittings and custom fabrication options. No more guessing or returns.

Key Features

Pipe measurement input (ID/OD) with unit toggle
Compatibility database of donuts and adapters for odd sizes
Direct ordering of correctly sized or custom donuts
Return/exchange handling integrated for wrong-size purchases

Target Users: Plumbers and pipefitters in home services and construction who deal with old or non-standard pipe sizes

Revenue Model: Commission on each donut ordered (10% markup) plus $19.99/month for a pro subscription with unlimited access to custom sizing and expedited shipping

Existing Solutions Mentioned

Fernco Compression Donut P33U-205

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