"For those not familiar with porcelain threadless, there have been 22 different U-numbers assigned. This doesn't mean that other styles don't exist, but if there are other styles, they have not been reported. Added to the pintype porcelain threadless is the porcelain block insulator, which dates back, at least, to 1848. This display has two styles of blocks, but, again, there may be more. Also included are specimens from the Southern Porcelain Company dump in South Carolina. Displayed for the first time together are the three known U-1960 "Hendersons", a most unique threadless "hat." And the U-986 was purchased at the show to complete the display.
Only one threadless style (U-978) was not on display. "This is the mystery insulator. It was reported to Jack Tod in the early 1970's. This piece is supposedly the property of the Smithsonian Institute, but recent searches at the museum have failed to locate the piece."