Silver and Deming drill bits are large size drill bits with reduced shanks that are ideal for situations where a bit diameter is greater than the capacity of a drill chuck. For example, if you need to bore a 5/8″ hole and your drill has a 1/2″ chuck, you’re going to be needing a Silver and Deming bit.
S&D bits have an overall length of 6″ and a reduced 1/2″ shank. Bits with 1/4″ shanks are available, but quite honestly they are best avoided unless the drilling task specifically calls for them.
Amazon stocks a decent selection of S&D bits, but you may want to check out an industrial supplier for an even better selection and perhaps lower prices.