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of Bristol and London
1789 Advert: 'PATENT BLOCKS, WHEELS, &c.
Messrs. JOHN GARNETT and Co. from the great difficulties attending a new Manufacture, have not hitherto been able to offer their INVENTION to the public, which saves nearly one-third of the men in all BLOCKS of PURCHASE, but as they have, from a variety of experiments made for two years past, discovered a Metallic Composition, whose tenacity and hardness promise a duration not before known for these articles, they can with confidence recommend them to all captains of ships, wheelwrights, &c. - The price not higher than what has been usually been given. - Specimens, and a number of certificates of their use, are to be seen at their Manufactory, No. 3, Narrow-street, Limehouse, London, or in College-street, Bristol.
Grindstones of all sizes that save one man's labour.
A Brass and Iron Foundery.' 
The catalogue of the 1919 Watt Centernary Exhibition including an example of early roller bearings. The exhibit comprised a horizontal shaft carrying a flywheel supported on roller bearings, stamped 'Garnett & Co, No. 1 Patent' (Patent dated 6 January 1797, granted to John Garnett of Bristol). Possibly submitted to Boulton and Watt with a view to their adoption of such bearings..
A description of the bearing was given in the Catalogue of the Mechanical Engineering Collection in the Science Museum. The shaft was 0.5" diameter, the six rollers were 0.375" diameter and 0.56" long, and were retained by a riveted cage. The catalogue also describes another Garnett & Co exhibit, a 7" diameter sheave for a ship's block fitted with a different form of Garnett's roller bearing. This has six rollers 0.625" dia and 0.875" long, with a central groove in which a slotted disc locates to keep the rollers in line.
The patent blocks, wheels, etc., in the 1789 advert obtained their claimed advantages from the use of roller bearings which reduced friction. The business was later carried on in College Street by Stephen Dobbins and Co. 'Patent Wheel and Block Manufactory, Brass and Iron Foundery; where Sugar Mills of every description are made, and all kinds of articles in the above branches for the West Indies.'
For more information on the roller bearings, see 'The House of Pinney and Garnetts Patent Rollers'
Garnett's blocks were the subject of competition between Walter Taylor and Messrs Garnett, Randall and Brent to supply the Royal Navy with rigging blocks, and a number of officers wrote a testimonial praising the superiority of Garnett's blocks.