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Gold-tone brass shaft coupling, 3mm by 4mm, with four install screws

Unique-Bargains

Unique-Bargains 3mm x 4mm Brass Motor Shaft Coupling Connector Adapter Joint Toy Part

SKU CH-E7W4-8WZEC

Brass motor shaft coupling joins 3 mm and 4 mm shafts with four included screws

  • Product typeToys - Replacement Parts
  • Brass construction resists corrosion for longer life
  • 3 mm to 4 mm bore joins mismatched shafts
  • Includes four install screws for immediate fitting
  • Compact 0.79" length fits tight RC chassis
  • Light 5 g mass keeps rotating weight low

What this coupling connects

This brass shaft coupling joins a 3 mm motor shaft to a 4 mm driven shaft in RC airplanes, boats and similar models. It is sold new as a single replacement part for hobbyists who need to repair or modify a drivetrain. The package includes one coupling and four installation screws.

Practical limits of the set-screw joint

The connector relies on two set screws per side, so alignment depends on accurate tightening rather than a keyed fit. Brass construction resists corrosion but can deform under high torque or sudden shock loads. The 2 mm thread diameter on the mounting screws limits the clamping force that can be applied safely.

Shaft diameter pair that decides fit

The coupling only works when one shaft measures 3 mm and the other measures 4 mm; any other combination will not engage the bores. Buyers with different shaft sizes need a different coupling.

How it compares

Measured against everything we stock in Toy Spare Parts & Connectors, at today’s prices. Recalculated every night.

Price $3.99
Cheaper than about 99% of the 69 comparable items (median $10.99).

Specifications

Product
Brand nameUnique Bargains
Product typeToys - Replacement Parts

Questions about this item

Which size coupling do I need for a 3 mm motor shaft and a 4 mm driven shaft?

This coupling is made for a 3 mm motor shaft on one end and a 4 mm driven shaft on the other, so it matches that exact pairing.

What does the 0.35 in (0.9 cm) diameter mean when the part is installed in a model?

The coupling body measures 0.35 in (0.9 cm) across, so it fits inside tight motor mounts and adds only a small profile to the drivetrain.

How do the 2 mm grub screws hold the shafts in practice?

Two 2 mm threaded holes accept the supplied grub screws; tightening them clamps each shaft securely without any keyway or pin.

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