This pen is a hybrid, of sorts. It is all 51 but there is no separate shell or clutch ring. This gives the pen a nice sleek look and is reminiscent of the 61 which has a thin clutch ring. The cap slides smoothly over the barrel with no metal-on-metal feel. The pen is a vacumatic filler like all early 51s and is made of a tranparent green lucite with matching jewels. The pen is offered with a sand blasted cap with engraved lines. This cap must be treated with care as the brushing, if handled roughly, will show scratches. The pen can be purchased alone for $700. Any, original, 51 cap will fit. The pen comes with a FIne nib.