The smallest increment of silver bullion available on the market would have to be the 1 gram silver bullion bars. One troy ounce of silver bullion contains just over 28 grams of silver. The one gram silver bar makes it very easy for the average person on a tight budget to start transferring some of their savings or wealth over to a real asset.
Silver bullion bars are flat and rectangular in shape which makes them very easy to store large quantities in a small amount of space or in a safe. The one gram silver bars are very tiny, a bit smaller than a dime. There value can be calculated by taking the current spot price and dividing it by 28.
So if spot price were $28, then each gram of silver bullion would be worth $1. Now buying it by the gram may allow a person with very little money access to investing in silver bullion, but it'll probably be a more expensive way of acquiring it when added up to a price per ounce or per every 28 one gram bars.
Let's say you are buying them for $1.25 each, well, that'd be $35 for every 28 grams. That's quite a bit more pricey when considering you can buy a one ounce American Silver Eagle for $2 over spot, which in this example would cost you $30. You can see how it would start adding up buying in one gram increments.
A much better strategy than buying 1 gram silver bullion bars from your local dealer would be to instead focus on buying one ounce silver bullion coins, bars, and rounds. Although they are more expensive per ounce than buying larger 100 or 500 ounce bars, they have a much better exit strategy. They will be much easier to sell when the time comes. They are more widely recognized and determining their value is easy as whatever the current spot price is, will be their current market value.