Lens Adapter Inquiry

[DanielAdAstra]

Hi,
I have a Pentax K1000 and have been shooting on a SMC Pentax-M 50mm lens and recently bought a new lens (Super-Takumar 50mm F1.4 M42 Screw Mount Thorium Lens) that I thought would fit but unfortunately seems to have slightly too small of a mount to fit. I was wondering if anybody would be able to inform me what kind of adapter I'd need to get to shoot on this lens.
Thanks!