Guide
What should an RFQ for custom quick-coupling components include so a CNC supplier can quote it correctly?
An RFQ for custom quick-coupling components is the package a build-to-print machine shop needs to price plugs, sockets, poppets, spring seats and lock sleeves: the drawing and model, the interface specification and its revision, the fluid and pressure conditions, who supplies the seals and springs, and who runs which tests. Put those on one or two pages and a CNC supplier can quote the metal parts without guessing what the coupling has to do.
By Saola Manufacturing engineering team · Published · Updated
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Why does a coupling part need more than a drawing in the RFQ?
Because a coupling is judged on what it does when mated, and a machining shop sees only the metal half of that. The RFQ has to carry the function, the interface and the test responsibilities that a part drawing cannot show.
A plug or socket body looks like a turned part with a groove, a thread and a hex. The same drawing could belong to a water-glycol cooling loop or a hydraulic circuit, and the supplier cannot tell from geometry alone which seal family, which fluid or which pressure the part will see. Those facts change the surface requirement on the sealing faces, the material and the cleanliness expectation, so they change the quote.
It also matters which features are fixed by an outside specification and which are left open. The Open Compute Project quick disconnect specification says it directly: where no dimension is given, the geometry is left to the discretion of the supplier. An RFQ that marks the controlled interface features and says which others the supplier may adjust avoids two failure modes: a shop that changes something you meant to freeze, and a shop that freezes something you would have let it optimize. The wider question of who owns design decisions on a print is covered in the build-to-print responsibility guide.
Which fields does a quick-coupling RFQ checklist need?
Use the fields the interchangeable-coupling world already buys with: size, half, termination, fluid, flow and pressure, temperature, seals, identification, specification revision and quantity. Then add the machining items a coupling checklist leaves out: material and condition, critical surfaces, and what inspection data you want back.
A published procurement checklist for OCP universal quick disconnects, written by an electronics distributor in its UQD buying guide (2025), asks the buyer for exactly these items. The fields are not specific to one standard, so they carry over to other coupling families. The table maps each field to what a machinist does with it.
| RFQ field | What to write | What the machine shop does with it |
|---|---|---|
| Size or series | The size code from your specification (the OCP document uses UQD02, UQD04, UQD06 and UQD08) | Sets the envelope, bore, seal gland size and the stock the supplier buys |
| Which half | Plug, socket, matched pair, or a component such as a poppet, spring seat or lock sleeve | Shows which dimensions are mating interface and which are internal |
| Termination | Thread or stud end, or hose barb, with size and class; wrench flats where fitted | Drives thread callouts, gauging and the tooling for flats and barbs |
| Fluid | Coolant or fluid chemistry and concentration | Decides material, passivation or coating, and whether seals are compatible |
| Flow, pressure and pressure drop | Rated flow, working pressure and the allowable pressure drop | Bore and port sizes, wall thickness and any flow-path surface requirement |
| Temperature | Operating range and shipping or storage range | Seal and material choice, and any thermal-fit consideration on mating parts |
| Seals and wetted materials | Elastomer family and who supplies it; wetted-material restrictions | Gland dimensions, sealing-surface roughness and whether the seal is free-issued |
| Identification | Marking text, color identification method and location | Marking process and where on the part it may go |
| Specification and revision | The exact document name, version and revision, plus any customer amendments | Tells the shop which dimension tables and notes govern |
| Quantity | Annual volume, release pattern and the size of a first order | Lets the supplier choose a process route that suits the volume |
Why name the specification and its revision instead of writing "compatible"?
Interchangeability is only claimed against a stated revision, and two suppliers can both say "compatible" while meaning different documents. Name the document, version and revision, and ask the supplier to confirm that same one in writing.
The distributor guide advises naming the exact specification and revision rather than writing "UQD v2 compatible", and checking that both suppliers explicitly claim conformity to the same revision when halves from two makers will be mated. The OCP document itself tells suppliers how to claim it: product literature should say that dimensional and performance requirements conform to the OCP UQD Specification, followed by the current version and revision (OCP UQD v2.0.0, section 11.1).
Revision changes show up in machined features. The version appendix of the OCP document warns that a version 1 plug end with minimal or no chamfer may damage the seals of both version 1 and version 2 sockets, so an end condition that was left undefined in one revision is now defined in the next. Status also moves: the distributor guide, which carries a January 2025 date, called version 2 a beta draft workstream, while the OCP document dated September 22, 2026 lists V2.0.0. Confirm the current status when you place the order, and write the edition year of any ISO test standard you cite; the ISO 18869:2017 record shows a revision in development.
Who supplies the seals, springs and test equipment on a build-to-print order?
Usually the buyer, or a source the buyer names, because performance depends on parts a machining shop does not design. State in the RFQ whether seals, springs, clips and test fixtures are free-issued, specified purchases, or left to the supplier.
Elastomer seals and springs are bought-in items whose material and hardness are design decisions. A machine shop's commitments are the metal: dimensions, sealing-surface texture, thread class, material and cleanliness. Where a seal arrives with the order, say so, and give the gland drawing source; where the supplier buys it, give the compound and a part number.
The same split applies to test results. The OCP specification defines a coupling-level performance report, covering burst, fluid loss, force to connect, pressure drop, seal washout, temperature cycling and mechanical cycling, and expects the coupling supplier to provide it on request (OCP UQD v2.0.0, section 9 and appendix 15.3). Those tests need assembled halves, seals and fixtures. The same section takes its sample size from ISO 18869, at least five samples per test, so a validation order needs enough machined pieces for that. A machining shop can return a dimensional report and material records for the metal parts; it cannot issue a coupling performance report, and an RFQ that asks for one will either be declined or answered with something other than what you expected.
Which machined features and surfaces should the RFQ flag as critical?
Flag the sealing and mating features, mark which dimensions an outside specification controls, and say which are free for the supplier to choose. For sealing surfaces, state the roughness cap and how it is checked.
The OCP tables show what a buyer-controlled interface looks like. Sealing and interoperability surfaces are called out to be machined to a 32 Ra maximum, the mating diameters carry linear tolerances given in its tables, and the plug end has a minimum-radius or equivalent chamfer (OCP UQD v2.0.0, tables 1 and 2 and figure 8). The note gives no roughness unit; confirm the reading with the specification owner, because 32 microinches is the usual American reading of that number. The figures show diameters, angles and linear tolerances, and no circularity or profile frame appears in the socket and plug figures.
The same document sets visual criteria that a machinist can act on: surface defects up to 0.3 mm² in some inspection zones and up to 1.0 mm² in others, no residual shavings or burrs, and no corrosion (OCP UQD v2.0.0, table 10). It requires stainless grades 303, 304, 304L, 316 or 316L for the plug tip and the cone and guide area (table 8). For a custom coupling, write the equivalent list: sealing faces and their roughness cap, burr-free zones, material grade and condition, and any surface treatment, with the drawing pages that show them. Surface callout syntax is explained in the surface finish symbol guide.
How should an RFQ describe a coupling part that runs in the tens of thousands a year?
State the annual volume, how it releases, and which characteristics you expect checked on every part versus by sample, then ask for the process route in the quote. At that volume a supplier chooses fixturing, tooling and inspection differently from a prototype run, and it can only do that if it knows the volume.
Ask for the quote at the annual volume and separately for a first order, and ask what the supplier would change in its process between the two. Name the first-article requirement up front, because for sealing parts it is the moment the metal meets the buyer's seals and springs; the first article inspection guide covers what to request. Say which dimensions the buyer will check on receipt, so the supplier can match its own inspection to yours.
Saola runs CNC turning and CNC milling at its lead plant in Vietnam, which suits turned bodies, poppets, sleeves and spring seats with milled flats or latch features. Surface treatments such as passivation are arranged through partner plants that Saola manages, and every quote names the production site and the country of origin. The machining RFQ preparation guide lists the general items every quote needs; this guide only adds the coupling-specific ones.
Frequently asked
Do I need to send the whole OCP document with the RFQ?
No. Give the specification name, version and revision, and list any amendments; the supplier can obtain the public document. Send the dimension tables and notes that govern your part if you want to be sure everyone reads the same page.
Can a machining supplier provide a coupling verification report?
Only for what it makes: a dimensional report and material records for the metal parts. A coupling-level performance report needs assembled halves, seals and test fixtures, so it comes from whoever assembles and tests them, or from a lab you appoint.
Should I send STEP, PDF or both?
Both. The model carries geometry; the drawing carries tolerances, surface notes and the list of controlled features. The STEP file versus 2D drawing guide explains why a model alone is not enough.
What if my coupling is not an OCP design?
Keep the same fields and replace the specification line with the document that governs your part, such as the flush-face hydraulic coupling standard ISO 16028:2023 (published March 2023) or your own drawing package. Name the edition year.
Who chooses the seal compound?
The design owner. Give the compound, hardness and supplier if known; if the supplier is to propose one, say that the proposal needs your approval before the first article.
Sources
- Open Compute Project, Universal Quick Disconnect (UQD) Specification, version 2.0.0, Open Compute Project, document dated September 22, 2026
- UQD connectors knowledge hub article, Dasenic, Dasenic, dated January 2025 (the page also notes a status check in July 2026)
- ISO 18869:2017, Hydraulic fluid power: test methods for couplings actuated with or without tools, ISO catalog record via Genorma, published July 2017
- ISO 16028:2023, Hydraulic fluid power: quick-action couplings, flush-face type, ISO catalog record via Genorma, published March 2023