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The Encyclopedia of Horology

Movement · Keyless watch mechanism

Rocking Bar keyless watch mechanism

Partially verified

Catalogued under object number 1920-539 in the Science Museum Group Collection, this spring-driven keyless watch mechanism dates to circa 1870. Sourced from the Bruno Roberts Collection, the brass movement features a rocking bar keyless mechanism and a detached lever escapement according to source records. The uncased movement is displayed with the dial side exposed, revealing its brass plate, motion work, rocking bar winding and setting assembly, central hands, and a small subsidiary pointer.

Dial side view of the uncased brass rocking bar keyless watch mechanism
Dial side view of the uncased brass rocking bar keyless watch mechanism — Science Museum Group. Rights pending — permission not yet requested. Original source

Catalogue identity

Source
collection.sciencemuseumgroup.org.uk
Category
Movement · Keyless watch mechanism
Maker / attribution
Not established
Reference
Not recorded
Catalogue / lot identifier
Source URL identifies the listing
Source-reported date
circa 1870
Country
Not established

Source-reported attribution and specifications are not independent authentication. A listing does not establish present ownership, current display, availability or permission to reproduce.

Object description

Identity and Provenance

This object is catalogued in the Science Museum Group Collection under object number 1920-539 with the title 'Rocking Bar keyless watch mechanism'. The institutional record classifies its type as 'spring-driven keyless watch mechanism , lever escapement and detached' and assigns an estimated date of 'circa 1870'. Provenance is noted through a credit line to the 'Bruno Roberts Collection'.

Neither a specific maker nor a place of origin is recorded in the museum documentation.

Evidence for this section
  • “Object Number: 1920-539”
  • “type: spring-driven keyless watch mechanism , lever escapement and detached”
  • “Made: circa 1870”
  • “credit: Bruno Roberts Collection”

Dial-Side Construction and Indications

The uncased circular brass movement plate is shown from the dial side without a dial plate mounted over the work. It features central pierced hour and minute hands mounted directly at the center arbor.

In the upper-left quadrant, a single blued steel pointer is fitted at a subsidiary dial location. In the upper-right section of the plate, faint hand-scratched watchmaker markings or numerals are visible on the metal surface.

Evidence for this section
  • “Circular brass movement plate shown from the dial side without a dial plate.”
  • “Central pierced hour and minute hands mounted at the center arbor.”
  • “A single blued steel pointer mounted at the subsidiary dial position in the upper-left quadrant.”
  • “Hand-scratched watchmaker markings or numerals visible in the upper-right section of the plate.”

Keyless Work and Mechanical Details

Visible on the dial side is an exposed rocking bar keyless mechanism consisting of steel winding and setting wheels, a pivoting rocking lever, and a jumper spring.

While the museum record describes the movement as having a detached lever escapement, only the dial side is shown in the provided photograph. The train, escapement, and balance assembly situated on the rear plate are not visible, leaving those structural details unobservable in the image.

Evidence for this section
  • “Exposed rocking bar keyless mechanism including steel winding and setting wheels, rocking lever, and jumper spring.”
  • “type: spring-driven keyless watch mechanism , lever escapement and detached”

Open research questions

  • What arrangement of the detached lever escapement and balance wheel is present on the unphotographed rear plate of movement 1920-539?
  • Can the hand-scratched numerals or watchmaker marks in the upper-right quadrant of the brass plate be deciphered to identify a servicing date or workshop reference?
  • What specific indication is governed by the blued steel pointer positioned in the upper-left quadrant?

Source evidence

Recorded claims and source quotations for Rocking Bar keyless watch mechanism
FieldSource-reported valueSource quotation
Object Number1920-539“Object Number: 1920-539”
Datecirca 1870“Made: circa 1870”
Typespring-driven keyless watch mechanism , lever escapement and detached“type: spring-driven keyless watch mechanism , lever escapement and detached”
CreditBruno Roberts Collection“credit: Bruno Roberts Collection”
CategoryTime Measurement“Category: Time Measurement”

Visible details

  • Circular brass movement plate shown from the dial side without a dial plate.
  • Exposed rocking bar keyless mechanism including steel winding and setting wheels, rocking lever, and jumper spring.
  • Central pierced hour and minute hands mounted at the center arbor.
  • A single blued steel pointer mounted at the subsidiary dial position in the upper-left quadrant.
  • Hand-scratched watchmaker markings or numerals visible in the upper-right section of the plate.

Research qualifications

  • The maker and country of origin are not recorded in the source.
  • Only the dial side of the uncased mechanism is shown in the provided photograph; the gear train and escapement on the rear plate are not visible.

Photograph identity and source facts were screened before import; rights clearance remains pending.

Consulted source

Rocking Bar keyless watch mechanism | Science Museum Group Collection

Reviewed 2026-10-21 · Record 282ef303f8

Terms in this record

Glossary explanations for terms named in this object’s record.