Screw threads as indicators of date
When there is doubt about the authenticity of an object, it may be closely scrutinised to match the technology used in its manufacture with what is known for the period.
Developments in the method of cutting screw threads and the adoption of standardised sizes are often informative. When threads are internal and cannot be unscrewed, X-radiography may be used.
Results of analysis
A genuine late C16th hand cut thread on the breech plug of an English snaphaunce pistol barrel on the left of the image and a supposed C15th hand-gun, fabricated using modern Whitworth thread shown on the right.
The development of screw-thread technology can provide good evidence of the age, life history and authenticity of many historic museum pieces.
Evidence from the X-radiograph of the thread holding this gun together provided key evidence for negotiating with the auction house that supplied it.