Custom Component Glossary: Key Terms Every Buyer Should Know 

One vague callout like "tight tolerance" or a wrong material grade can add weeks to your lead time or give you parts that pass inspection and still fail in the field, so this custom component glossary puts custom manufacturing terminology in plain English for your engineering and purchasing teams. 

Why Does Custom Component Terminology Matter When Sourcing Parts? 

Miscommunication costs 

Say an RFQ asks for "tight tolerance" with no number. One shop quotes ±0.005 in, another ±0.0005 in, and now you're requoting. Or a drawing lists 304 stainless when the job needed 440C hardness. Same story: rejected first articles, or a part that wears out early. Most of it traces back to custom manufacturing terminology that nobody defined. 

Bridging engineering and procurement 

Engineers think in tolerances and grades. Buyers think in price breaks and lead times. When both sides know the same procurement terms for custom components, quotes come back faster and with fewer questions. 

How to use this glossary 

We've ordered it the way terms show up in real life: drawing first, then the quote, then inspection. Think of it as machining terms for buyers and engineers in one place. Read it straight through or skip to what you need. 

What Drawing and Design Terms Should Buyers Understand? 

GD&T (Geometric Dimensioning and Tolerancing) per ASME Y14.5 

A symbol-based language for controlling a part's shape, orientation, and location. Think of it as the core of any GD&T terms explained list. Used well, it gives shops room to work where the part doesn't care, which often lowers cost. 

Datum and datum reference frame 

A datum is a reference point, line, or plane that measurements start from. Change the datum and the same part can pass or fail. 

Feature control frame 

That little box on a drawing holding a symbol, a tolerance value, and datum letters. It's the piece of GD&T terms explained that shops read first, because it tells the machinist and the inspector exactly how to check a feature. 

Critical-to-function (CTF) dimension 

A size that has to be right for the part to work. Flag these. You'll pay for tight control only where it counts. 

Tolerance stack-up 

The combined variation when several parts go together. Each part can be "in tolerance" and the assembly still won't fit. It's one of the machining terms for buyers that saves the most headaches. 

Revision level and drawing control 

The letter or number showing which drawing version is current. Quote from an old revision and you'll get the wrong part, fast. 

STEP / IGES file formats for quoting 

Neutral 3D files most shops can open. They show up in most RFQ terms for custom parts, and they speed up quoting, but the drawing still governs tolerances. 

What Do Tolerance and Fit Terms Mean on a Custom Part Drawing? 

Bilateral vs. unilateral tolerance 

Bilateral allows variation both ways (1.000 ±0.002 in). Unilateral allows it one way only (+0.004/-0.000 in). It changes where a machinist aims. These tolerance and fit definitions matter on every drawing. 

ISO 286 IT grades (IT5 to IT11) and what they cost to hold 

IT5 is very tight, IT11 is loose. Every step tighter usually means slower cuts, better tooling, and more inspection, so the price climbs. 

Hole-basis vs. shaft-basis systems 

Hole-basis fixes the hole size and adjusts the shaft to get the fit. Shaft-basis flips that. Hole-basis is more common since holes are harder to fine-tune, and it's a staple of machining terms for buyers. 

Clearance fit (e.g., H7/g6), transition fit (H7/k6), and interference fit (H7/p6) 

Clearance leaves a gap, so parts move freely. Transition could land either way. Interference makes the shaft slightly bigger than the hole, so it grips. 

Press fit and shrink fit 

A press fit forces parts together. A shrink fit heats or chills one part first. The method you pick affects assembly cost and risk. 

Title block default tolerances (e.g., ±0.005 in on three-place decimals) 

The catch-all rule for any dimension without its own tolerance. It may cover features you never meant to leave loose, so read it. This bit of custom manufacturing terminology hides the most surprises.

 

What Bearing-Specific Terms Appear in Custom Component Specs? 

ABEC 1 to 9 and ISO tolerance classes (P0, P6, P5, P4, P2) 

Precision ratings, and a core entry in any bearing terminology glossary. Higher ABEC numbers mean tighter, while ISO P-classes run the opposite way. Tighter costs more, and plenty of jobs don't need it. 

Radial internal clearance (C2, CN, C3, C4) 

The tiny gap inside a bearing. CN is normal, C3 is looser. Pick wrong and heat or fit problems shorten bearing life. 

Preload (light, medium, heavy) 

Load applied on purpose to take out internal play. It boosts stiffness and accuracy, but too much just makes heat. 

Dynamic load rating (C) and static load rating (C₀) 

C is what a bearing handles while turning. C₀ is what it handles sitting still. Use both to match a bearing to real loads, a key idea in any bearing terminology glossary. 

L10 bearing life 

The life that 90% of identical bearings reach or beat. It helps you compare options and plan maintenance. 

Shaft and housing fit recommendations for bearing seats 

Suggested fits for the surfaces a bearing sits on. These tolerance and fit definitions apply to seats too, and a sloppy seat causes creep, noise, and early wear. 

What Material Specification Terms Should Buyers Know? 

AISI/SAE designations: 1045, 4140, 52100 bearing steel 

1045 is a general-purpose carbon steel, 4140 is a tougher alloy, and 52100 is the classic bearing steel. The number drives strength, hardness, and price. These material specification terms are the first thing to check on a quote. 

Stainless grades: 303, 304, 316, 17-4 PH, 440C 

303 machines easily, 304 resists corrosion, 316 handles harsher chemicals, 17-4 PH is strong and heat-treatable, and 440C hardens for wear. Wrong grade, rust or wear. 

Aluminum tempers: 6061-T6, 7075-T6 

6061-T6 is the everyday choice. 7075-T6 is stronger.  

Engineering plastics: UHMW-PE, acetal (POM), PEEK, nylon 

UHMW-PE resists wear and impact, acetal holds size, PEEK handles heat and chemicals, nylon absorbs shock. See our UHMW wear parts article. 

Hardness scales: Rockwell C (HRC) vs. Brinell (HB) 

HRC (like HRC 58 to 62) rates hard steels. Brinell covers softer metals. Among the machining terms for buyers, hardness matters because it affects wear life and machining time. 

Tensile strength vs. yield strength 

Tensile is the load at break. Yield is where the part bends and stays bent. For design, yield is usually the number that matters. 

Mill test report (MTR) and material certification 

Paperwork from the mill showing what the metal is made of. It's your proof you got the grade you paid for, and one more of the material specification terms worth memorizing. 

What Manufacturing and Finishing Terms Come Up in Quotes? 

CNC turning, CNC milling, 5-axis machining, Swiss-type turning 

Turning spins the part, milling spins the tool. 5-axis reaches complex shapes in one setup. Swiss-type suits small, slim parts. This is everyday custom manufacturing terminology, and fewer setups mean less time and error. More on custom machined parts. 

Wire EDM and precision grinding 

EDM cuts hard metal with electrical sparks. Grinding delivers very tight sizes and smooth surfaces. Both cost more but hit numbers turning can't, so they're worth knowing among machining terms for buyers. 

Heat treatment: through-hardening vs. case hardening vs. induction hardening 

Through-hardening hardens the whole part. Case hardening does the outer layer. Induction hardens just a chosen zone. Each trades wear resistance against toughness. 

Surface finish and Ra values (e.g., Ra 63 µin standard machined vs. Ra 16 µin ground) 

Surface finish Ra explained in one line: Ra is average surface roughness, and a lower number is smoother. Smoother finishes cost more, but they cut wear on moving parts. 

Finishes: passivation, black oxide, Type II and Type III anodizing, zinc plating 

Passivation helps stainless resist corrosion, black oxide adds light protection, anodizing coats aluminum, zinc protects steel. Coatings add lead time and can change part size. 

Deburring and edge break 

Removing burrs and sharp edges. Leave it off the drawing and it may show up as extra work. Check our seals and retaining rings page too. 

What Quality and Inspection Terms Should Buyers Recognize? 

First article inspection (FAI) and FAI report 

A full check of the first part against every drawing requirement, written up in a report. That's the first article inspection definition in short, and it catches problems before you pay for the whole run. 

CMM (coordinate measuring machine) inspection 

A machine touches points on the part and measures it. You get exact, repeatable data, even on complex features. 

Process capability (Cpk ≥ 1.33) and statistical process control (SPC) 

Cpk shows how well a process stays inside limits, and 1.33 is a common target. SPC tracks it over time. Together they tell you whether good parts are luck or control. 

Certificate of conformance (CoC) 

A signed statement that the parts meet your order. It's one of those procurement terms for custom components that plenty of quality systems require. 

Lot traceability 

Tracing a part back to its material and process records. If something goes wrong, you can find every affected part. 

PPAP (Production Part Approval Process) for OEM programs 

Proof that a supplier can make the part right, every time, before production starts. It builds on the first article inspection definition with much deeper documentation. 

ISO 9001 quality management systems 

A common standard for documented, repeatable processes. It's a decent sign a shop runs a tight operation. 

Nonconformance report (NCR) and corrective action (CAPA) 

An NCR records a defect. CAPA fixes the root cause. How a supplier handles these says a lot. 

What Procurement and Commercial Terms Appear in Custom Part Quotes? 

RFQ (request for quote) and what a complete RFQ package includes 

Send the drawing at current revision, material, quantity, finish, inspection needs, and delivery date. These RFQ terms for custom parts are your starting point. Missing details mean guesses, and guesses mean requotes. 

EAU (estimated annual usage) 

How many parts you expect to buy in a year. Shops use it to plan material and set pricing. 

MOQ (minimum order quantity) and price breaks 

MOQ is the smallest run a shop will do. Price breaks drop the unit price as volume climbs. Both are procurement terms for custom components you'll see on nearly every quote. 

NRE (non-recurring engineering) and tooling charges 

One-time fees for programming, fixtures, or special tools. On a big run they spread thin. 

Blanket purchase order and scheduled releases 

One order for a total quantity, released in batches. You get steady supply and often better pricing. 

Lead time: quoted vs. actual, and expedite fees 

Quoted is the promise, actual is what happens. Rushing costs extra, and late parts can cost more than the parts themselves. 

Incoterms (EXW, FOB, DDP) and landed cost 

Incoterms say who pays for shipping and duties. Landed cost is the full price at your dock. Of all the RFQ terms for custom parts, this pair explains why the cheapest quote isn't always the cheapest part. 

How Do These Terms Help Buyers Weigh Cost, Lead Time, and Quality Tradeoffs? 

Tolerance vs. cost 

Tightening from IT9 to IT6 can multiply machining cost. Justify it only on CTF features and use your tolerance and fit definitions to decide where it counts. 

MOQ and EAU vs. unit price 

Bigger orders cut per-part cost, but extra stock ties up cash and shelf space. Knowing your procurement terms for custom components helps you find the balance. 

Lead time vs. safety stock 

If you're expediting all the time, holding a buffer may be cheaper. 

Inspection level vs. risk 

Match FAI, CMM reports, and certs to how critical the part is. A guard doesn't need the paperwork of a bearing seat, so lean on the first article inspection definition and pick what fits. 

Landed cost vs. quoted price 

Freight, duties, delays, and quality escapes can wipe out offshore savings.  

Why Choose Bearings Direct for Custom Components? 

Engineering review of drawings and RFQs 

We flag ambiguous callouts before we quote, not after you've got the wrong parts. Our team speaks custom manufacturing terminology fluently. 

Broad capability 

Custom bearings, machined parts, UHMW wear parts, seals, and retaining rings. Browse custom bearing components at Bearings Direct.  

Documentation support 

Material certs that back up your material specification terms, plus CoCs, FAI reports, and lot traceability, all handled. 

Responsive quoting and reliable lead times 

Quick answers and dates we stick to. 

FAQ: Custom Component Terms 

1. What is a custom component glossary? It's a list of custom manufacturing terminology used on drawings, quotes, and inspection reports for custom parts, so buyers and engineers read the same thing. 

2. What does "tight tolerance" mean? Nothing, until you give a number. Write it out, like ±0.001 in or IT6. 

3. Clearance fit or interference fit? Those are two key tolerance and fit definitions. Clearance leaves a gap so parts move. Interference makes the shaft slightly larger than the hole so parts grip. 

4. Why do a first article inspection? It checks the first part against the whole drawing, catching mistakes before a full production run. 

5. What does Ra mean? Surface finish Ra explained simply: Ra is average surface roughness. Ra 16 µin is smoother than Ra 63 µin. 

6. What belongs in a complete RFQ? Current drawing, material, quantity, EAU, finish, inspection and certification needs, and your delivery date. These are the RFQ terms for custom parts every buyer should know. 

7. What's the difference between MOQ and EAU? MOQ is the smallest order a shop will run. EAU is how many parts you expect to use per year. Both are procurement terms for custom components. 

8. What's a certificate of conformance? A signed document saying your parts meet the order requirements. 

9. When do I need PPAP? Usually on OEM programs, especially automotive, where suppliers must prove their process is capable before production. 

10. Why does landed cost matter? It includes freight, duties, and delays, so it shows what a part really costs you. It's one of the machining terms for buyers that often gets overlooked. 

Get Expert Help with Your Next Custom Component RFQ 

Got a drawing you're not sure about? Send it over. Our engineers will review it, flag anything unclear, and help you get an accurate quote. Submit your RFQ or browse the custom components catalog at Bearings Direct.