Are you looking for an earlier reference for "gadget" than the 1918 one listed in the OED? When I looked for information on the history of this tool, it looked like some historians date it back to 1760 and others date it to Mid 19th century. In addition, the British called it a "gadget" while the Americans used the term "snap" or variants of that word.
I am attaching an article by glass historian David Watts on the gadget. He might be a good person to contact for more information (https://www.glasscircle.org/), or you might want to contact the Broadfield House Glass Museum (https://www.dudley.gov.uk/see-and-do/museums/glass-museum/contact-us/). Their records for British glassmaking may be more complete than ours. I didn't find any references to gadget earlier than the 1918 listed in the OED, but it would take lots of looking through glassmaking treatises, factory publications or notebooks from the 19th century. I am also attaching a list of publications on English glass of the 19th century, in case that will be useful to you, as well as a list of early texts on glassmaking.
