page_title: Mainspring gauge
section_title: Dennison "US Standard" gauges
hierarchical_section_title: Mainspring gauge / Dennison "US Standard" gauges
caption_attribution_description: English: Dennison "US Standard" combined mainspring gauge
context_page_description: Mainspring gauges were used to measure the sizes of watch mainsprings so that replacement springs could be ordered from a supply house.
  Mainsprings are characterised by their strength and height.
context_section_description: About 1840 Aaron Lufkin Dennison devised a gauge "upon which all the different parts of a watch could be accurately measured", Figure 3. Later this became known as the "US Standard" gauge. The edges have the usual notches for mainspring heights (based on the Imperial inch, but there is no obvious way to determine mainspring strength, except perhaps by barrel diameter using one of the three scales on the top left (which are Imperial inch scales in 1/64 and 1/32 divisions).
  Over time, this gauge was simplified and reduced to being purely a mainspring gauge, Figure 4. Only the height notches remain and a thickness slit gauge added to it. The slit gauge is also based on the Imperial inch, but it often has metric equivalents which are crude approximations.
caption: Figure 3: Dennison combined gauge. Actual size 150 × 19 mm.
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