This clips is a reproduction GM NOS clips used by GM on many of the larger cars of the early to mid 60’s. Such as the Chevy Impala, Buick and the Pontiac.
This clip is known to be used on Buicks . It is new and the measurements are shown in the picture. When installed they press into a bathrub shapped hole in the body where the molding would be positioned. These clips are not being made today so what I have is what I have until I find some more at some later date.