Injection Mold Parts Explained: The Complete Chinese-English Glossary (150+ Components)

Every injection mold component across all 10 systems, in Chinese and English — plus the mistranslations that appear in real quotes from Asian tool shops.

PLASTIC ENCLOSURES

Peakingtech

8/13/20269 min read

exploded view of a plastic injection mold

You get a DFM report back from your tool shop in Dongguan. It says your part needs "two line positions and one inclined top." Your quote lists four "division cylinders." Somewhere in the email chain, someone keeps mentioning the "water gap."

None of those are real English terms. They're literal translations of Chinese shop-floor vocabulary — 行位, 斜顶, 司筒, 水口 — and they refer to a slide, a lifter, an ejector sleeve, and the gate/runner system respectively. Every one of them affects your tooling cost.

This is the reference we send clients who are quoting tooling in Asia for the first time. It covers all ten systems of a plastic injection mold, roughly 150 components, with the Chinese name, the correct English name, what the part actually does, and — where it matters — what it does to your budget.

Bookmark it. Or skip to the section you need:

Molding system — the parts that form your plastic
Mold base system — the steel frame everything bolts into
Gating and feed system — how plastic gets in
Cooling system — how heat gets out
Hot runner system — the expensive upgrade
Core-pulling and slide system — undercuts, and what they cost
Ejection system — how the part comes out
Fasteners and hardware
Electrical, hydraulic and pneumatic
Auxiliary components

Then: the translation traps, which parts actually drive cost, and which parts wear out.

First, the two halves

Before the tables, the single most important piece of vocabulary.

A mold has two halves. In English we call them the cavity (fixed half, attached to the injection side of the machine) and the core (moving half, attached to the clamp side). In Chinese, they're 前模 (qián mú, "front mold") and 后模 (hòu mú, "rear mold").

Front = cavity. Rear = core. Almost everything else in a mold is described by which half it lives in, so if you get these two straight, half the confusion disappears.

1. Molding System

成型系统 — the steel that actually shapes your part

These are the surfaces your plastic touches. Everything here is polished, precision-machined, and expensive to change after T0.

Worth knowing: item 10, the exchangeable insert, is one of the most underused cost savers in hardware. If you have three product variants that differ only in a logo, a port cut-out, or a button count, you may not need three tools. You may need one tool and three inserts.

2. Mold Base System

模胚系统 — the frame

The mold base (模胚 or 模架) is the standardized steel skeleton. Western engineers know DME, HASCO, and Futaba. In Shenzhen and Dongguan, the default is LKM (龙记, Lung Kee) — a perfectly good standard, but one that will be unfamiliar if you've only worked with US or European toolmakers. Ask which standard is being quoted; it affects spare part availability for the life of the tool.

Worth knowing: guide pins (导柱) align the mold roughly. They are not precision locators. For tight-tolerance or thin-wall parts, you also want taper interlocks or side locks — see section 10. If a quote for a precision part has no interlocks in it, ask why.

3. Gating and Feed System

浇注系统 — how the plastic gets in

Worth knowing: 水口 (shuǐ kǒu) is the single most-mistranslated term in Chinese moldmaking. Literally "water mouth," it shows up in emails as "water gap," "water port," or just "water." It means the gate and runner system — the sprue, runners, and gate, plus the plastic waste they produce. If your supplier asks about "water gap position," they're asking where you'll accept a gate mark on your part. That's a cosmetic decision you should make deliberately, not one you should let the tool shop make for you.

4. Cooling System

冷却系统 — how the heat gets out

Cooling is 60–80% of cycle time on most parts. It's also the thing most commonly under-engineered on cheap tooling, because a customer comparing quotes can't see a cooling layout but can see a price.

Note that Chinese shops say 运水 (yùn shuǐ, "moving water") where English says "cooling lines" or "water lines."

Worth knowing: ask for a cooling layout drawing as a deliverable, separate from the mold assembly drawing. On a well-designed tool the lines follow the part geometry, sit at a consistent distance from the molding surface, and use baffles or bubblers to reach deep cores. On a poorly designed one they're straight holes drilled wherever there was room. The second kind is cheaper to build and will cost you five seconds of cycle time on every shot for the life of the tool.

5. Hot Runner System

热流道系统 — the expensive upgrade

Worth knowing: hot runner is a genuine step change in tooling cost — typically several thousand USD upward, plus a temperature controller that may or may not be included in the quote. Ask explicitly whether the controller is in scope. It frequently isn't.

The decision is volume-driven. Hot runner eliminates runner waste and shortens cycle time, so at high volume it pays for itself in material and cycle savings. At low volume it's an expensive way to buy complexity — more heaters to fail, more zones to tune, longer startup. Somewhere in the 100k–250k annual units range is where the math usually flips, but it depends heavily on resin cost and part weight. If you're molding an engineering resin at 40g a shot, it flips much earlier. If you're molding PP at 5g, much later.

6. Core-Pulling and Slide System

抽芯系统 — undercuts, and what they cost

This is the section to read if you care about tooling budget. Every entry here exists because your part has a feature that can't come straight out of the mold.

Worth knowing: a slide (行位) and a lifter (斜顶) both solve undercuts, but they aren't interchangeable.

Slides handle undercuts on the outside of the part — a side USB port, a snap window in a wall, a side button. Driven by an angle pin, they retract as the mold opens.
Lifters handle undercuts on the inside — an internal snap hook, an inward-facing boss. They ride on the ejector plate at an angle, so they move inward as the part is pushed out. Lifters live in section 7 because they're part of the ejection stroke.

Slides are more expensive than lifters. Both are more expensive than no undercut. If you're at the CAD stage, the highest-leverage conversation you can have with your tool shop is not "how much per slide" but "can we redesign this feature away." A snap hook rotated 90 degrees, or a boss moved to a parting line, can delete a slide from the quote entirely.

Items 12–16 (gear, rack, sprocket, chain, bearing) all belong to unscrewing molds — tooling that rotates cores out of threaded features like bottle caps or lens barrels. If your part has an internal thread and your quote doesn't mention any of these, verify how the thread is being formed. The alternative is a collapsible core, which is a different cost structure again.

7. Ejection System

顶出系统 — how the part comes out

Worth knowing: ejector pins leave marks. Always. On a cosmetic part, "where will the ejector pin marks be" is a question you answer during DFM, not one you discover at T1. Ask for an ejection layout drawing showing pin positions, and check them against your A-surfaces.

If your part is a deep, thin-walled box, expect a conversation about air poppet valves (气顶) or a stripper plate (推板) instead of pins — pins will simply punch through or distort the wall.

8. Fasteners and Hardware

紧固零件

Note: The following is compiled from Peakingtech's own tooling documentation and reflects standard practice at Shenzhen and Dongguan mold shops. Terminology varies slightly between shops; treat these as the common forms.

Worth knowing: item 3. Screws clamp; dowels locate. If an insert is fitted with screws only and no dowel pins, it will shift in service. On a precision part this shows up as a step at the insert line, and it will get worse over the tool's life.

9. Electrical, Hydraulic and Pneumatic

电气、液压、气动零件

Worth knowing: item 4 is a safety and tool-protection item, not a nice-to-have. A hydraulic slide that fails to retract before the mold closes will destroy itself and take the cavity with it. Limit switches are cheap. Confirm they're in the quote for any hydraulically actuated mold.

Item 7, the cycle counter, is how you know when preventive maintenance is due and how you verify shot counts against a contract manufacturer's reporting. Ask for one. Almost nobody does.

10. Auxiliary Components

其它辅助零件

Worth knowing: the nameplate (item 2) and the mold storage protocol are the two things clients forget to specify and later regret. If you own the tool, your name should be on it, along with your part number. When you eventually move production, you want that tool identifiable in a warehouse of four hundred others.

The Translation Traps

These are the terms that cause the most confusion in real correspondence. If you hear one of these on a call or see it in an email, this is what's meant.

That last group — 走胶, 缩水, 披锋 — aren't parts, but they'll appear in the same emails and cause the same confusion, so they're worth having here.

Which Parts Actually Drive Your Tooling Cost

Not all 150 components move the number. These are the ones that do, in rough order of impact:

1. Cavity count. Doubling cavities doesn't double tool cost, but it's the largest single lever. Driven by your annual volume and cycle time, not by preference.

2. Slides (行位). Each one adds a meaningful increment — the slide body, base, retainer, angle pin, locking block, and wear plates, plus the machining and fitting time. Four slides on a part is a very different tool from zero.

3. Hot runner (热流道). A step change, not an increment. Includes hardware and, usually separately, a temperature controller.

4. Lifters (斜顶). Cheaper than slides but not free. Each adds components and fitting time to the ejection system.

5. Steel grade. P20 versus H13 versus stainless (e.g. 2316 / 420) changes both material cost and machining time. Glass-filled resins are abrasive and will eat a soft tool; if you're molding 30% GF nylon, hardened steel isn't optional.

6. Surface finish. SPI A1 mirror polish and a heavy texture are both expensive, for opposite reasons. A standard machined or light bead-blast finish is the cheap default.

7. Unscrewing mechanisms. Gears, racks, and motors for threaded features. Significant, and worth designing around if you can.

We've deliberately not published dollar figures here, because slide cost varies by size, steel, and shop by a factor of three or more, and a stale number is worse than none. If you want a real range for your specific geometry, send us the CAD.

Which Parts Wear Out, and When

Tooling is not a one-time purchase. Budget for these:

These are broad ranges and depend heavily on resin, cycle time, and maintenance discipline. A tool running abrasive glass-filled material at a fast cycle with no scheduled maintenance will hit the low end of every row. Ask your molder for their PM schedule and their shot counter reading — if they can't produce either, that's information.

Frequently Asked Questions

What is the difference between a slide and a lifter in an injection mold? A slide (行位) forms and releases undercuts on the outside of a part and is driven by an angle pin as the mold opens. A lifter (斜顶) forms and releases undercuts on the inside of a part and rides on the ejector plate, moving inward as the part is ejected. Slides are generally more expensive to build than lifters. Both add cost compared with a part designed without undercuts.

What does "water gap" mean in a Chinese mold quote? It's a literal translation of 水口 (shuǐ kǒu) and means the gate and runner system — where plastic enters the cavity, and the plastic waste that system produces. "Water gap position" means gate location, which is a decision that affects both cosmetics and how the part fills.

What is a mold base, and which standard should I use? The mold base (模胚) is the standardized steel frame that holds all the working components. Common standards are DME and HASCO in the West, Futaba in Japan, and LKM (龙记) in southern China. LKM is the default for most Shenzhen and Dongguan shops and is a good standard, but confirm which one is quoted — it determines spare part sourcing for the life of the tool.

How many cavities should my mold have? It depends on annual volume, cycle time, machine tonnage available, and part cost target. As a rough starting point: under 10,000 units a year, single cavity is usually right; 50,000–200,000 typically justifies two to four cavities; above that, eight or sixteen becomes worth modeling. The correct answer comes from running the math on tool cost amortization against per-part cycle savings, not from a rule of thumb.

Do I need a hot runner? Usually not at prototype or early production volumes. Hot runner eliminates runner waste and shortens cycle time, which pays back at higher volumes — often somewhere in the 100,000–250,000 annual unit range, though this shifts significantly with part weight and resin cost. Expensive engineering resins and heavy parts move the break-even much earlier.

Why does my quote list parts I don't recognize? Most likely because they're machine-translated from Chinese. Use the translation traps table above. If a term isn't there, send us the quote and we'll identify it.

Who owns the mold — me or the factory? Whoever the contract says. This is worth settling in writing before tooling starts, along with where the tool is stored, who maintains it, and what happens if you move production. A tool you paid for but can't physically retrieve is a common and avoidable problem.

Working With a Tool Shop You Can't Read

The vocabulary gap is real, but it's the smallest of the problems it causes. The bigger one is that when a founder can't fully read a DFM report, they tend to approve it — and undercuts, gate positions, and ejector marks get decided by the tool shop, optimizing for what's easy to build rather than what's right for the product.

At Peakingtech we sit on the Shenzhen side of that gap. We review tooling quotes, translate DFM reports into decisions you can actually make, and manage tool builds through T0, T1, and into production.

Reviewing a tooling quote you can't fully read? Send it over. We'll mark it up in English and tell you what's missing — no charge, no obligation.

Last updated: August 2026. Terminology reflects common usage in Shenzhen and Dongguan mold shops; regional variation exists. Sections 8–10 compiled from Peakingtech tooling documentation.