Start at the port, not at the catalogue. Most fitting problems on a new air line are not product failures — they are selection gaps that survived all the way from the first sketch to installation day. Reayon Pneumatic builds push-in fittings, and the returns we see share one root cause: nobody ran a complete pneumatic fitting selection pass before the drawing was released. This article gives design engineers a 7-step path that turns port symbols into a complete, testable fittings BOM.
Two Ways to Fill a Fittings BOM — and What Each One Costs Later
Every project picks one of two paths, whether the team admits it or not.
Path A: order as the build proceeds. The installer runs tube, hits a junction, and calls for whatever connector seems right that day. The line gets built. Then the costs start: three body styles where one would do, brass fittings inside a washdown zone, a second order in week three, and a splice someone made with the wrong tube size that hisses for the life of the machine.
Path B: one selection pass before release. The engineer walks the circuit once, fixes the tube ODs, pressure limits, thread families and material zones, and issues a fittings BOM with part numbers. The installer connects instead of deciding. Retrofits shrink, and spare-parts stock stays small.
Path B takes about an hour on a typical machine drawing. Path A usually costs two to three weeks of scattered reorders on a new line. The 7 steps below are that pass, in order.
The 7-Step Pass From Port Symbols to Part Numbers
Fix the tube OD system first. Count every tube run on the drawing and choose metric or inch — not both. A mixed drawing forces two collet families and doubles the SKU count. If you inherit a mixed machine, mark each run with its OD in writing. Our guide on metric and inch tube sizes explains why the two must never share a fitting.
Set the pressure envelope per branch. Most shop-air circuits live between 0 and 150 PSI. Write the working pressure on each branch, and derate any run that passes a hot zone — standard push-in fittings are rated for service up to about 60 °C. Mark vacuum branches separately, because they need fittings that hold negative pressure.
Assign a thread family per port. Match each port symbol to BSPP, BSPT, NPT or metric, and note the size. Do not let the drawing carry two thread conventions for the same valve family. If the port markings are unclear, our product pages and thread identification guide cover how to read BSPP from BSPT before ordering.
Choose the body style per location. Straight unions for in-line runs, elbows where the tube must turn inside a cabinet, tees at distribution points, bulkheads wherever the line crosses a panel. Every style change should trace to a physical reason on the drawing, not to installer preference.
Mark material zones. Split the circuit into static branches inside enclosures and exposed runs near moving parts. That single line on the drawing decides where plastic fittings are fine and where nickel-plated brass earns its price.
Add spares at 10 percent. Take each part number, add 10 percent, and round up to whole boxes. Weight the extra stock toward service points and operator stations, where fittings get disconnected and reconnected every week.
Convert the list to part numbers and test samples. A BOM line that reads "8 mm tee, plastic" is not a BOM line yet. Fix the model code, then bench-test three samples of anything new before you release the drawing.
Where Plastic and Nickel-Plated Brass Fit in the Same BOM
The material step is where most engineers over-order or under-order. The practical split is simple.
Zone
Body material
Typical branch
Why
Inside cabinets, static runs
Plastic push-in
Signal lines, actuator feeds with no contact
Low cost, light, fast insertion
Exposed runs, moving equipment
Nickel-plated brass
Slides, grippers, operator stations
Resists impact, vibration and knock-ons
Washdown or corrosive spots
Nickel-plated brass
Food and packaging lines
Plating protects the brass body
Reayon Pneumatic supplies both ends of that table from one factory: the plastic push-fit range for cabinet work, and the MP Series nickel-plated brass fittings for exposed and washdown zones. Both seal on the same tube OD, so one tube size can run through the whole machine with no plumbing change.
The tubing choice follows the same logic. PU tubing stays flexible around moving parts; nylon holds its shape on long static runs. If you are unsure which pairing to draw, the guide on choosing fittings for PU and nylon tubing walks through it step by step.
What Path A Actually Costs You Later
Run the numbers on a typical 60-fitting machine and the contrast is stark.
Reorder cycles. Ad-hoc ordering usually triggers two to three follow-up purchases as installers discover missing body styles. Each cycle adds freight and waiting time.
SKU sprawl. Three installers ordering by feel will spec three tee styles where one does the job. Your spares cabinet inherits all of them.
Hidden leaks. A fitting forced into the wrong zone — plastic where the tube flexes all day — weeps slowly and shows up as compressor duty cycle, not as an alarm.
Redraw churn. Every improvised junction eventually has to be documented. Reworking drawings after build costs more than an hour of selection before release.
None of this shows on a quote sheet. That is exactly why it survives into production.
How to Check the BOM Before You Release the Drawing
Before you sign off, run this five-minute audit against your own drawing:
Every port symbol carries OD, unit system and thread — no blanks.
Each branch shows its working pressure, and hot or vacuum zones are marked.
Material zones appear on the drawing, not just in an email.
Every BOM line ends in a part number, not a description.
New part numbers have passed the sample bench test: insertion by hand, leak check at working pressure, and 100 insertion cycles for anything disconnected in service.
Reayon Pneumatic supports this audit directly: send us the circuit description, and we will return the fitting list with model codes, pressure notes and sample fittings for bench testing before you commit to production volumes.
Frequently Asked Questions
What working pressure should I design to for push-in pneumatic fittings?
Standard plastic and brass push-in fittings carry a working range of about 0 to 150 PSI (up to 1.0 MPa) at room temperature. Design each branch to its real working pressure, not the catalogue maximum, and derate for higher ambient or line temperatures. Vacuum branches need fittings rated for negative pressure as well.
How many spare fittings should a line BOM include?
A practical rule is 10 percent of each part number, rounded up to at least one full box for the sizes used at service points. Add extra stock for the fittings installed near moving parts and operator stations, because those see the most wear and get swapped most often.
Can I mix plastic and brass push-in fittings on the same air line?
Yes, and most well-designed lines do. Use plastic push-in fittings for static branches inside cabinets, and nickel-plated brass fittings where tubing is exposed to vibration, mechanical contact or washdown. Both seal on the same tube outside diameter, so they can share one tube size without any plumbing change.
What should the drawing show so purchasing orders the right fittings?
Each port symbol should carry the tube outside diameter with the unit system, the thread family and size, and the material zone marking where it matters. A note listing the fitting part numbers per zone removes the last ambiguity and lets purchasing order a complete BOM in one pass.
How do I validate a fitting before releasing the fittings BOM?
Bench-test three samples of each new part number. Check insertion force by hand, hold the joint at working pressure for a leak test, and run at least 100 insertion and removal cycles on the sizes that will be disconnected in service. A fitting that passes all three checks is safe to release to production.
Send the Drawing, Get a Marked-Up Fitting List
Send Reayon Pneumatic your tube sizes, branch pressures and material zones, and we will return a fittings BOM with part numbers, sample fittings and factory-direct pricing. Start from our product catalogue or reach the engineering team through the contact page.
