I wonder how the Pilot design team came up with the idea for the SPRINTER… a one-piece body comprised of a stout steel spring coil with just enough uncompressed at the tail end to function as the tension for the button.
There are versions of the all-steel version with brightly painted steel clips but they are rarer than hen’s teeth. So for now, this is it for my SPRINTER journey. 
I love how the spring is integrated into the body like that. I wish I had a pen version.
@drifand I was perfectly fine not collecting these, and then you go and post these pictures.
Well… I guess I need to collect those now.
Fantastic photos!
I’ve also wondered about the design, how it was conceived, and what kinds of prototypes might’ve been experimented with before achieving this design. Maybe someone who was thinking, “how do we avoid the typical eraser cap unsightly abrasions from all the pressing?” 
It’s such a novel concept. And so well executed. The math employed such that the coils are uniform AND spaced just enough such that when the body is fully compressed, the clutch is opened wide as normally would be achieved with a traditional design. The teardrop nose was a design very similar to the one on the shaker H-515… but better. I wonder how difficult it was to machine it… because it was never used again.
Here’s one of the catalog pages:
I captured photos from several auctions featuring the other colors with the tear drop nose cone and made montage images:
Auction wise, these were NOT high on the collector radar for years, and back about 8~12 years ago you could snap up a Sprinter without a high cost… with some exceptions. The rare color ones were always sought after.
Here are some old Sprinter auctions I looked up and captured, sharing here for collection references.
