Views: 0 Author: Tonney Shao Publish Time: 2026-06-29 Origin: Abery Mold
"Can you hold precision on this part?" is one of the most common — and most poorly answered — questions in injection molding sourcing. Almost every supplier will say yes. Far fewer can tell you exactly what tolerance they can hold, on which features, in which material, and back it up with inspection data. This guide breaks down what precision injection molding actually means, what drives how tight a tolerance is realistically achievable, and how to ask better questions when you're evaluating a supplier.
"Precision" gets used loosely in marketing, so it helps to break it into the three things buyers usually actually care about:
Tight dimensional tolerances — how closely the finished part's dimensions match the design drawing, part after part.
Tight cosmetic and surface finish control — consistent gloss, texture, or surface quality with no visible defects like sink marks, flow lines, or warpage in appearance-critical areas.
Repeatability across production — the ability to hold those dimensions and finish consistently across thousands or hundreds of thousands of shots, not just on the first few parts off the tool.
A part can be "precise" in one of these senses and not the others. A supplier might nail dimensional accuracy on the first article but drift over a long production run because of tool wear, or hold dimensions fine but struggle with consistent cosmetic finish. When you're sourcing for a precision application, it's worth being specific about which of these three actually matters most for your part.
It helps to have a general sense of what's typical in the industry before you start a supplier conversation, so you know whether a quote or claim sounds reasonable.
As a general industry reference point, commercial-grade injection molded parts are often held to tolerances in the range of roughly ±0.1mm to ±0.2mm, while precision or high-precision work can target tighter tolerances than that — but exactly how tight depends heavily on the specific material, wall thickness, and part geometry involved. Thin-walled parts, parts with long unsupported features, or parts in materials with high shrinkage rates are inherently harder to hold tight tolerances on than a simple, thick-walled part in a low-shrinkage material.
We're intentionally not putting a single guaranteed number here, because a responsible supplier shouldn't either — not without seeing your actual part drawing. The honest, useful question to ask any supplier isn't "can you do precision parts," it's: "What tolerance can you hold on this specific feature, in this specific material, and can you document that in the quote?"
Several factors — not just the molding machine — determine how tight a tolerance is realistically achievable on a given part:
Mold steel choice. Harder, more wear-resistant steels hold their precision longer across high shot counts than softer steels, which can degrade over time.
Tool build quality. How precisely the mold cavity itself was machined and finished sets the ceiling for what the part can ever achieve — no machine setting can compensate for a poorly built tool.
Material shrinkage behavior. Every plastic resin shrinks by a different amount as it cools, and shrinkage isn't always perfectly uniform across a complex part. This has to be accounted for in the mold design itself, not fixed later.
Part geometry and wall thickness. Uniform wall thickness, generous radii, and well-planned gate locations all make it easier to hold tight tolerances. Abrupt thickness changes and thin, unsupported features make it harder.
Machine repeatability. The injection molding machine needs to repeat its process parameters — pressure, temperature, cooling time — shot after shot. Machine condition and process control discipline matter here.
In-house metrology and inspection capability. A supplier can only prove they're holding tolerance if they can actually measure it — which means access to proper inspection equipment like a CMM (coordinate measuring machine), not just calipers.
Since "we do precision parts" is nearly meaningless on its own, here's a more useful way to evaluate a supplier's actual capability:
What to Ask For | Why It Matters |
A first-article inspection (FAI) report | Shows actual measured dimensions against your drawing on real parts, not a verbal promise |
Tolerance capability by feature type | A supplier might hold ±0.05mm on a simple boss but not on a long, thin snap-fit — ask feature by feature, not for one blanket number |
In-house measurement equipment list | CMM, optical comparators, and calibrated gauges indicate a supplier can actually verify what they build, rather than eyeballing it |
Documented tolerances in the quote | If a tolerance commitment isn't written into your quote or purchase order, it isn't really a commitment |
Process control documentation | Ask whether they track shot-to-shot consistency, not just measure the first few parts and move on |
If a supplier can't produce an FAI report or explain what measurement equipment they use, that's a meaningful signal — regardless of how confidently precision is described in their marketing materials.
Abery's engineering team is structured to support this kind of tolerance-sensitive work end to end. Our team includes 6 dedicated mold designers and 2 CNC programmers who work through tool design and machining together, and 8 QC engineers responsible for inspection and process verification. On the equipment side, our shop runs CNC, EDM, and WEDM machines alongside our injection molding presses — this combination matters for precision work specifically because EDM and WEDM (wire-cut EDM) processes can achieve mold cavity details and finishes that standard CNC machining alone often can't reach, particularly for sharp internal corners, fine features, and hardened tool steel.
That said, we'd rather be direct than vague: the right way to find out what tolerance Abery — or any supplier — can hold on your specific part is to send the drawing and ask for it in writing as part of the quote, along with a first-article inspection plan. That's a more useful answer than any general percentage or number we could put in a blog post.
Identify which dimensions are truly critical vs. nominal/non-critical on your drawing
Specify tolerance requirements by feature, not as a single blanket tolerance for the whole part
Ask the supplier for their measurement/inspection equipment list
Request a first-article inspection report as part of the quote process
Confirm tolerance commitments are written into the quote or PO, not just discussed verbally
Ask how the supplier plans to control shrinkage and warpage risk in your specific material
Real precision in injection molding comes from a combination of tool steel choice, build quality, material science, machine discipline, and verified inspection — not from a single number on a website. If you're sourcing a tolerance-sensitive part, the most productive thing you can do is ask your supplier for tolerance capability by feature, backed by first-article inspection data, before you commit.
If you have a precision part and want a straight assessment of what tolerance is realistically achievable, send your drawing to Abery's engineering team at tonney@a-mold.com or message +86 139 2521 4356 on WhatsApp. You can also learn more on our dedicated precision injection molding page.
Written by Tonney Shao, CEO of Abery Mold. Tonney has spent 16 years helping overseas buyers source injection molds and plastic parts from China, and has personally overseen mold projects for clients including Schneider Electric and Honda's supply chain. Contact: tonney@a-mold.com | WhatsApp: +86 139 2521 4356
