Early Biltwell flattops from the 1920s. All were cheaply made, but the mechanism used is a relatively durable. Most of these came from a single ebay purchase I made a few years ago. It was advertised as being a box of pencils from a closed drug store.
These pencils accept standard .046" leads.
Later Biltwells. The three on the left have a Welsh mechanism. Identical flattops were marked Starite. Although Biltwell was a lower tier manufacturer, the later offerings were better quality pieces. The pearl and white example is particularly nice.