The left side shows mainstream SMD single-turn trimmers—Bourns 3314J, Panasonic EVM3E, and Copal ST-32—commonly used in SMT production for one-time factory calibration.

Summary
SMD trimmer potentiometers (e.g., 3314) and multi-turn trimmer potentiometers (e.g., 3381/3296/3386) serve the same purpose: fine resistance adjustment. The split is how and how often you trim.
SMD favors one-time factory set-and-lock in compact SMT flows, while multi-turn types enable repeatable, ultra-fine calibration with better serviceability.
Each spans a different kind of “breadth”: SMD across the manufacturing ecosystem, multi-turn across the precision-calibration ecosystem.

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1) What they are

• SMD trimmers (mostly single-turn): Surface-mount, top/side adjust, low profile, reflow-compatible; ideal for one-time production trims.
• Multi-turn trimmers (10–25 turns): Mainly THT with lead-screw/gear mechanisms; high resolution and repeatable; ideal for precision calibration and service.

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2) Construction & process

SMD is compact with short travel and fits SMT + reflow (fast takt, lower BOM/manufacturing cost).
Multi-turn is larger with fine travel; typically wave/hand soldered and friendlier to end-of-line or field trims.

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3) Performance focus

• Resolution: Single-turn SMD targets an acceptable window; multi-turn lets you land precisely.
• Power: SMD ~0.05–0.25 W (@70 °C); multi-turn ~0.25–0.5 W (series-dependent).
• Vibration / reliability: SMD’s low profile helps; multi-turn should be adhesive-locked or sealed for stability and moisture protection.

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4) Where they’re actually used

SMD fits (one-time trim / compact / full SMT):

• One-time factory trim then lock with adhesive/conformal coating.
• Consumer, wearables, compact PSUs, dense digital boards where space and throughput dominate.

Multi-turn fits (repeatable calibration / ultra-fine granularity):

• Instruments & bridges: zero/span trims with repeatable setpoint return.
• Precision analog: op-amp offset/bias, reference dividers, filter bandwidth.
• Industrial control: servo zero, PID seeds, relay trips, PSU Vout/ILIM.
• Medical/aerospace: periodic recalibration with strict records.
• Audio/low-freq analog: channel balance, level matching, long-term bias stability.

Takeaway: SMD spans the broader manufacturing front; multi-turn spans the deeper precision-calibration front.

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5) Quick spec snapshot

Dimension	SMD trimmers (e.g., 3314)	Multi-turn trimmers (e.g., 3381/3296)
Mounting	SMD, reflow	THT, wave/hand
Turns	Single-turn (short travel)	10–25 turns (lead-screw/gear)
Typical power	0.05–0.25 W	0.25–0.5 W
Profile	Low, compact	Taller, larger
Adjustment frequency	One-time set	Repeatable fine trims
Vibration	Low-profile advantage	Stable when locked/sealed
Service	Rarely touched after set	Easy to recalibrate/service

Note: Values are typical ranges; always verify against target datasheets.

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6) Quick Selection

Topic	Guidance
Process path	Full-SMT and tight space → pick SMD trimmer
Trim pattern	One-time set & lock → SMD; need >10 turns with repeatable fine trims → multi-turn
Power & environment	Low–mid power, dense layout → SMD; higher headroom/thermal stability or higher ambient → multi-turn (lock/seal after trim)
Vibration & service	High vibration/shock → SMD; if multi-turn is required → adhesive/conformal coat and sealed versions for serviceability
One-liner	Throughput/compact → SMD; repeatable ultra-fine calibration/serviceability → multi-turn

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7) Taxonomy (for internal links)

By mounting

• SMD trimmers (single-turn): 3314J (top-adjust, 3×3 mm), 3314G (side-adjust, 3×3 mm), TC33 (top-adjust, 3×3 mm), SM-42 (7×7 mm low-profile)
• THT trimmers (single-turn): 3362 (top/side-adjust), 3386 (vertical/horizontal)
• THT trimmers (multi-turn): 3381 (lead-screw, 10–25 turns), 3296 (sealed multi-turn)

Typical footprints

• SMD:
  • ~3–4 mm (e.g., COPAL ST-32)
  • ~3.7–3.9 mm (e.g., HDK VG039 / VG039NCHXT)
  • ~3.5 mm (e.g., Panasonic EVM3E / EVM3ESX)
  • ~4.6–5.0 mm, low profile (e.g., Bourns 3314J)
  • 7×7 mm (e.g., SM-42 low-profile)
• THT: vertical (lead pitch 2.5–5.0 mm), horizontal (lead pitch 2.5–5.0 mm)