SPG (KOSDAQ: 058610): Korea's Only Full-Lineup Precision Reducer Maker
SPG spent most of its fifty-year history making fan motors for refrigerators and geared motors for factory automation — unglamorous, thin-margin, high-volume work. Then robotics happened, and the company discovered it was sitting on something rare: the only Korean manufacturer building planetary, harmonic and RV cycloidal reducers all under one roof, precisely the three types a humanoid robot needs across its different joints.
Who they are
Founded in 1973 as Sungshin P & Ind and renamed SPG in 2000, the company built its business on two low-margin, high-volume product lines: geared motors for automation equipment (roughly 30% of sales, around 10% operating margin) and fan motors for white goods like refrigerators (roughly 65% of sales, only 2–3% margin). That's a mature, unglamorous industrial business that has generated steady if unexciting cash flow for decades.
What changes the story is a small but fast-growing third line: precision reducers for robots. SPG is, uniquely among Korean manufacturers, capable of producing all three major precision reducer types in volume — planetary, SH harmonic, and SR RV cycloidal — giving it a rare full-lineup position in a market that Japan's Harmonic Drive Systems and Nabtesco have historically split between them by specialising in one type each.
That completeness matters because a single humanoid robot uses different reducer types across its body: cycloidal for high-torque hip and knee joints, harmonic for precision wrist and hand joints, planetary for simpler applications. A robot builder that wants a single domestic supplier covering the whole joint spec sheet has, in Korea, essentially one option.
What they do
The precision reducer business has been growing steadily off a small base: revenue rose from KRW 7.6 billion in 2023 to KRW 10.2 billion in 2024 to KRW 14.0 billion in 2025, still only around 4% of total company revenue but climbing every year. SPG supplies these reducers into Rainbow Robotics' collaborative robots and dual-arm systems, and into semiconductor production-line automation equipment.
The Rainbow Robotics relationship is the one to watch most closely: SPG generated an estimated KRW 16 billion of revenue last year from reducer supply to Rainbow, a Samsung Electronics-backed platform that is scaling its Sejong facility toward mass production in the second half of 2026. As that facility converts from pilot to volume production, SPG's reducer content should scale roughly in proportion — a direct, disclosed link between one customer's manufacturing ramp and SPG's own growth.
Beyond Rainbow, SPG signed a memorandum of understanding with LG Science Park in late 2025 to collaborate on high-efficiency actuator and reducer technology, and has begun supplying reducers for defense unmanned-systems programs and MRO (maintenance, repair, overhaul) parts replacement at overseas factories — a diversification of the customer base beyond a single robot platform.
How they make money
2025 full-year results: revenue of KRW 341.7 billion, down 12.1% year over year, and operating profit of KRW 17.9 billion. The revenue decline reflects a deliberate mix shift — SPG has been cutting low-margin, China-facing geared motor and fan motor volume in favour of higher-value precision reducers and industrial motors, a trade that showed up clearly in first-quarter 2026 results: revenue down 13.4% year over year to KRW 80.8 billion, but operating profit up 9.7% to KRW 4.5 billion and net income up 11.1%.
That range of estimates — some analysts closer to KRW 356 billion, others near KRW 419 billion, for the same fiscal year — is itself a signal: SPG's near-term financial outcome depends heavily on how fast Rainbow's Sejong plant actually ramps, which is not fully within SPG's own control.
Where it sits in the value chain
SPG sits in Stage 2 — Precision reducers & gearing, positioned as the domestic Korean alternative to importing reducers from Japan. As Korean robot builders like Rainbow Robotics and Doosan Robotics scale, a local, full-lineup supplier reduces both lead time and currency exposure relative to sourcing from Harmonic Drive Systems or Nabtesco.
SPG's position also illustrates a pattern repeating across several stages of this chain: an established industrial manufacturer with decades of adjacent mechanical engineering experience — motors, gearing, precision machining — pivoting a small, fast-growing division toward robotics while the legacy business continues funding operations. Hyundai Mobis and Sanhua Intelligent Controls follow the same shape one stage over, in actuators.
The bigger trend
SPG is a small-capitalisation proxy for a much larger question: can Korea build a domestic precision-component supply chain for robotics, or will Korean robot builders remain dependent on Japanese and increasingly Chinese reducer imports? SPG's full-lineup capability is a genuine answer to that question, but it is still a small company whose 2026 financial outcome is unusually concentrated in the fortunes of a single customer's factory ramp.
The stock's 52-week range — from roughly ₩19,130 to ₩94,200 in 2025 alone — captures how much of SPG's current valuation is priced on the robotics growth story rather than the mature motor business that still generates the bulk of revenue. That volatility should temper how much confidence anyone places in near-term analyst estimates for this name specifically.
What to watch
- Rainbow Robotics' Sejong facility mass-production conversion in H2 2026 — the single biggest near-term driver of SPG's reducer revenue.
- Precision reducer revenue's share of total sales, tracked against the company's own 25–30% five-year target.
- Progress on the LG Science Park actuator and reducer technology collaboration.
- Any expansion of the defense unmanned-systems reducer supply beyond initial volumes.
- Continued mix shift away from low-margin China-facing geared and fan motor business.
Related companies
🇰🇷SPG's largest disclosed robotics customer, and the growth engine behind its reducer segment.
🇯🇵The Japanese import SPG's domestic full-lineup position competes against.
🇰🇷Fellow Korean industrial supplier making the same automotive-to-robotics pivot, one stage downstream.
FAQ
What makes SPG unusual among reducer makers?
It is the only Korean manufacturer producing all three major precision reducer types — planetary, harmonic, and RV cycloidal — in volume. Most competitors, including Japan's Harmonic Drive Systems and Nabtesco, specialise in one reducer type each, so a robot builder wanting a single domestic full-lineup supplier in Korea has essentially one option.
How much of SPG's revenue comes from robotics?
Around 4% as of 2025, though it has grown every year, from KRW 7.6 billion in 2023 to KRW 14.0 billion in 2025. The company's stated long-term target is to grow that to 25–30% of total revenue within five years, driven primarily by robot reducer supply.
Who is SPG's main robotics customer?
Rainbow Robotics, the Samsung Electronics-backed cobot and humanoid platform maker, which SPG supplies for its collaborative and dual-arm robots. SPG generated an estimated KRW 16 billion from this relationship in the most recent disclosed year, and growth is expected to track Rainbow's Sejong facility mass-production ramp in the second half of 2026.
Is SPG profitable?
Yes, though total revenue has been declining as the company deliberately cuts low-margin fan and geared motor volume in favour of higher-value products. 2025 operating profit was KRW 17.9 billion on revenue of KRW 341.7 billion, and first-quarter 2026 operating profit rose 9.7% year over year even as revenue fell 13.4%, reflecting the mix improvement.