Chuck Wilts homemade knife blade pitons c.1950s
​Some are stamped "YC" from Yvon Chouinards personal gear.
Link to Chuck Wilts history. In the writing it is mentioned that Chuck invented the Knife Blade piton.... which actually Chuck created his version a Vertical piton and named it a Knife Blade. Possibly Chuck came up with the name "Knife Blade."
This is a photo taken by William "DOLT" Feuerer of the gear used on the El Capitan Nose Route in Yosemite 1956/1957. On the very bottom of the photo on the left side is a Chuck Wilts piton.
A few Chuck Wilts pitons shown in this collection.  Photo: Jerry Gallwas collection - Props John Middendorf
1954 Sierra Club bulletin
Chuck Wilts homemade bolt hanger