As I was learning Rashi's take on the sugyah of a katan's machshava, at one point I felt that Rashi is telling us that regarding hechsher l'tumah it is the machsava to form a k'li that is machshir it rather than the fact that it is a finished product, similar to &ki yutan that the thought process is what actually is machshir it. However I connot retrace my thought process any more or remember what made me come up with this nobel approach. Have you ever heard of such a sevorah

Thanks

Eliezer Perl