A #J is actually 0.277" diameter.
There is a whole series of drill bits that are identified by letters rather than numbers or fractions. They typically fall between the common fractional sizes. A #J would be a little smaller than 9/32", and a bit bigger than a 17/64" bit. If you search for drill bit sizes, or for lettered bits specifically, you will find plenty of charts listing out the sizes in order, with corresponding decimal equivalents.
