When Two Systems Meet at a Flange
Flange adapters exist because equipment never comes from one catalogue. A pump ends in a four-bolt flange, the line it feeds is threaded pipe. A metric machine port has to meet ANSI pipework. An instrument needs a flanged connection the manufacturer never offered. Catalogue adapters cover the popular pipe classes — the moment your bolt circle, bore or thread steps outside them, the part stops existing.
EKINSUN machines that part. We make custom flange adapters — the bolt pattern measured from your actual flange, the other side machined as a thread, weld hub, register spigot or second pattern — cut from solid 304/316 stainless, carbon steel or aluminium, one piece or a batch, quoted within 24 hours.
Looking for complete flanges rather than an adapter — blinds, pipe flanges, motor mounts? See custom machined flanges. For thread-to-thread conversion without a bolt pattern, see thread adapters.
One Flange Face — Four Ways to Finish the Other Side
Every flange adapter is really the same question: the bolt pattern is fixed by the mating part, so what does the other side need to be?
| Other side | What it does | Typical use |
|---|---|---|
| Female or male thread | Flange-to-pipe or flange-to-fitting in one piece — BSP, NPT or metric, with the right seal form | Pump outlets to threaded line, instrument ports, drain and vent points |
| Weld hub / stub | A machined hub sized for butt or socket welding to your pipe | Fabricated skids and tanks where the pipe is welded, not threaded |
| Register spigot | A turned pilot that centres the adapter in the mating bore before the bolts go in | Motor and gearbox mounting, rotating equipment where concentricity matters |
| Second bolt pattern | Two different bolt circles in one plate, through-bored to the line size | Metric machine flange to ANSI valve, obsolete pattern to modern equipment |
The Non-Standard Bolt Circle Problem
Catalogue flange adapters assume catalogue flanges — ANSI 150, DIN PN16, the common pipe sizes. Plenty of real equipment doesn't play along: OEM pumps with proprietary patterns, older machines built to standards nobody stocks anymore, or flanges that were simply drilled to suit the machine they sat on. If you're holding a flange whose pattern matches nothing, the pattern itself is all we need — bolt circle diameter, hole count, hole size and bore. Measure it, photograph it with a rule in frame, or post us the mating part. We machine the adapter to bolt straight on.
Obsolete equipment flange? If the machine is old and the original adapter is broken or missing, we reproduce it from the remains or from the two parts it joined — see obsolete & discontinued parts and how we reverse engineer.
Materials for Flange Adapters
304 / 316 stainless
Corrosive media, washdown, marine and chemical service; 316L where welding follows. Machined from solid bar — no casting porosity under the gasket face.
316 machining →Carbon steel
General pipework, structural duty and hydraulic skids — strength at the best cost, plated or painted as needed.
Carbon steel →Aluminium
Light-duty and low-pressure adapters where weight matters — vacuum lines, enclosures, instrumentation.
6061 machining →From the Mating Part to a Finished Adapter
Send the pattern
The bolt circle, hole count, hole size and bore — or the mating flange itself, or the broken adapter.
We draw it and you confirm
Bolt pattern, facing, thread or hub and gasket surface specified on a drawing we rebuild free. No CAD needed →
Machine, face, inspect
Turned and drilled from solid, gasket face machined to spec, hole positions checked before shipping.
What to Send for a Fast Quote
- Bolt circle diameter, number of holes and hole size — or photos of the mating flange with a rule
- What the other side must be: thread size and standard, weld hub for what pipe, or the second pattern
- Medium, pressure and temperature, so we pick material and facing
- Gasket type if you know it (flat, spiral-wound, O-ring groove)
- Quantity and delivery country
Frequently Asked Questions
Yes — that's the usual reason to have one machined. Give us the bolt circle diameter, hole count and hole size (or send the mating flange, even a rubbing of it) and we machine the adapter to bolt straight onto it, with the thread or hub your other side needs.
Yes. A flange-to-thread adapter carries the bolt pattern on one face and a female or male thread — BSP, NPT or metric — in the centre. We machine the thread to the standard your pipework uses and face the flange for the gasket you specify.
Yes — a pattern-to-pattern adapter plate with one bolt circle on each side, through-bored to your line size. Common when metric equipment meets ANSI pipework, or when an obsolete machine flange must mate with a modern pump or valve.
304 and 316/316L stainless for corrosive or washdown service, carbon steel for structural and general pipework, aluminium where weight matters and pressure doesn't. Machined from solid — no casting porosity — with EN 10204 3.1 certificates on request.
Yes. Send the old adapter, or the flange and the part it must connect to, and we measure the bolt circle, bore, thread and facing, rebuild the drawing free of charge and machine a replacement. No CAD file or part number needed.
Get a Flange Adapter Quoted
The bolt pattern and what the other side must be — that's enough. Engineers reply in 24h.
// Qty & price
1 pc
Sample price
Prove the fit first
3–10
Unit price drops
Setup cost shared
10+
Best price
All tiers quoted upfront
- →No distributor — you pay the maker directly
- →CAD saved after first order — reorder anytime at lower unit price