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America on the Move
Collection Exhibition Themes
Staybolt taps (2)
Catalog #: 2002.0075.02, .03, Accession #: 2002.0075
Currently on display
From the Smithsonian Collection
Tool used by boilermakers in steam locomotive repair shops, to thread holes for firebox staybolts. See General History, above.
Physical Description
Hard tool-making steel, with cutting threads. Both taps 18" L.
Used in locomotive boiler work everywhere.
Gift of National Park Service

Part of a small array of hand tools displayed in "America On The Move" - such tools were used in the inspection and repair of steam locomotives. Light repairs on steam locomotives were usually done in roundhouses at the many small locomotive terminals throughout a railroad's system; heavy repairs were done in a large, centralized repair shop serving the whole system (often referred to as the "Back Shop"). Most of these tools date from the early- to the mid-20th century, roughly 1900-1955.

"Taps" are designed to cut threads into drilled holes, so that threaded bolts or threaded machine screws can be screwed in.

Staybolt taps were used by boilermakers when installing or repairing the fireboxes of steam locomotives. The long tap was screwed into pre-drilled holes through the boiler's outer steel shell and into the steel firebox within the boiler. The tap cut threads into the hole in the outer boiler shell and also into a corresponding hole in the firebox. The tapped hole permitted a "staybolt" to be inserted and screwed into place; each staybolt held the boiler shell and the firebox firmly together.

(Staybolts had "timed" threads at each end, so that the staybolt would screw simultaneously, and without binding, into the tapped thread in the outer boiler shell and into the same tapped thread in the firebox steel.)

In a given boiler, hundreds of staybolts thus supported the firebox from collapse under the high steam pressure within the boiler. After a staybolt was screwed into position, its end was hammered over. Replacing staybolts was a large part of a boilermaker's work in a steam locomotive shop.

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