Sigma 75-300mm question

Hello Pentaxians!

I recently ordered a used zoom lens and I can't mount it to my camera (Pentax K1). The lens is an old Sigma APO 75-300 f4-5. It has a plastic flange (or something) extending past the mount base plate (as pictured). The plastic over-lap will not allow the lens to make full contact with the camera. I'm will likely just file the plastic down, but I thought I would consult professional advise first . Any help would be much appreciated. Thanks, Rick

that does not look like a Pentax K mount at all. It should look like this link if you try too hard mounting it, it could damage the camera

No, that's not compatible.

If you were sold it as Pentax compatible you have a case to return it to the seller.

that is not pentax just checked mine and it is totaly wrong

I've only had fleeting use of them so can't be entirely certain, but that looks a bit like a Nikon F-Mount?

As stated by others above, it's sadly not a Pentax fit, I'm afraid.

An example of an F-Mount Nikon lens
:

Interesting. Thanks for all the replies. Good to know it's not Pentax. I'll try and return the lens.