This research project, reported in three parts, focuses on Henry Nock's 'screwless lock', or, as it is called in documents at the time of its manufacture, the 'Duke's Lock', in the most important production variant of this novel and sophisticated design. This is the 5.5in long 'Type 2' Duke's Lock, as fitted to the final design iteration of the Board of Ordnance's Duke of Richmond's Musket (DoRM), namely its rammer-to-the-muzzle (RTM) version. The three papers report the results of the first published systematic assessment of the Duke's Lock's interchangeability. No statement has yet been found in archival material to suggest that the lock is, or was considered to be, interchangeable, or that it has interchangeable components, but the authors of many secondary works think that it was, and therefore we set out to investigate this important matter systematically. This, the first paper, presents the findings of a five-lock component exchange experiment, which permits 20 component interchange tests. Measurements of key dimensions have also been made to assist in understanding the fits at which interchangeability was achieved. The exchange experiments establish that from 50% to 100% of the lock's small components are interchangeable, with two especially surprising results: all cocks exchange on the large centres of the locks (20/20 or 100%), and all sears which can be tested are found to exchange between bents (17/17 or 100%). Tests assessing the complete assembly of all components in the lock thickness direction, omitting problematic individual components, show success rates of 16/20 (80%) and 14/20 (70%). The results of this process are placed in a material context through metallographic analysis of components of a less well-preserved Board of Ordnance 5.5in Duke's Lock by Nock, and, for comparison, on an almost contemporary Board of Ordnance India Pattern Musket lock. The analysis has revealed that many components of the Duke's Lock are made of steel rather than wrought iron, and that, for the centres and some other key components, these steels were selected because their properties suited machine turning, and this reflects Nock's expert use of lathes within a factory that was using steam power by 1795. The analysis is supported by the disassembly and technical examination of some locks, including one that was partially completed, to analyse methods of construction. As regards archival sources, we have built upon Howard Blackmore's seminal paper of 1956 by discovering additional archival data in the Ordnance Bill books, specifically the records of transactions with Nock's executors after his death in 1804, to as late as 1808. This has allowed an improved understanding of the number of locks supplied and the uses to which they were put. The Ordnance Bill Books show that Nock delivered 12,010 Duke's Locks in only 29 months, between 4 July 1793 and 25 November 1795. Together the papers explore how Henry Nock was able to produce the remarkable figure of 12,010 interchangeable locks in 1793–95, five years before the production of 10,000 interchangeable locks was achieved in France by Honoré Blanc, who is widely regarded as the first in this field. Significantly, Nock's work also preceded that of Samuel Bentham, Mark Brunel and Henry Maudslay on the famous machines for making interchangeable components – in wood – for the blocks required for ships' rigging; the three principals began their work on this in 1799. The present three-part study not only firmly establishes Henry Nock's leading position in the field of firearm development but also as one of the pioneers of interchangeable manufacture at scale in engineering more widely, both nationally and internationally. Part 2 uses studies of the marks on a sample of 25 locks to reveal more about the manufacturing system for Duke's Lock and how the people within the system were organised. The final paper, Part 3, discusses the small changes in design and inspection made during and after production that are revealed in the earlier Parts, and also how the design of George Bolton's later patent lock was influenced by Nock's work and the experience of his workmen. [ABSTRACT FROM AUTHOR]