I have two hard rubber Swan Split levers. One has the standard U shaped metal parts for the lever. The other, however, is quite plain, and quite solid.
The pens are the same size, caps can interchange between pens. The clipless with solid lever is marked 4SF, and the shiny chrome furniture pen is marked 2SF.
Oddly, the 4 SF has a standard feed, cut off at a right angle internally, but the 2 SF has a feed seen on eyedroppers with the conical tip on the inside. Both have the early marking with arrows telling the user to screw down tightly. The marking is under the chrome clip on the 2SF.