Originally posted by SelrahCharleS Oh yep, you're right. It's the K version (well I assume since it just says "SMC Pentax 1:2.8 24mm" on the front).
I believe the SMC Pentax 2.8/24mm continued to be sold during the "M" times. I also believe that the same optical layout stated the same in the Pentax-A version with electric contacts. I think the best of the bunch (waiting for the beautiful FA 2/24mm) was the first 24mm in PK mount: the SMC Pentax 3.5/24mm. I have both, but I didn't have enough time to test the latter in a proper way. I have the A version since the eighties. I found it good but not exceptional.
Taking the chance to post an update about my latest cheap, Covid-affected purchases.
For little more than a tenner I bought an old soviet Sonnar clone. It's the Jupiter-8 2/5cm in LTM mount. It has the nice tab on the focusing ring typical of that vintage (1959) and the original front cap. Unfortunately the filter thread is badly ruined, though the damage sustained doesn't seem to affect the optical performance. I compared it to a Jupiter-3 1.5/50mm (1967) in spotless condition I bought at the time of the Leica M5. The two lenses share a similar (beautiful) "Sonnar bokeh" and perform well enough wide open, but the Jupiter-3 has a clear edge over the slower, less sophisticated alternative. It's a real pity both lenses don't have a place on Pentax DSLR's, cause I used them on a Pana GX8 m4/3 with very good results. However, I must say that these lenses scream for full format. A 50% crop doesn't give them chance to fully shine.
The other poor man's purchase has been a job lot of lens hoods. Together with a few really ugly bits, the package consisted in two nice Super Takumar era hoods, plus a rare pearl: the non standard push-in hood for the Tamron SP 17mm! Very few such lenses are sold with the dedicated hood, and all the replacement hoods I tried (including a Vivitar push-in with set screw) proved to be a failure. All of them showed strong vignetting. Now I have the two original hoods for both the Tamron 17mm and the Pentax-A 2.8/20mm. The latter is kind of unwieldy, but works great. Strong wide angles need proper hoods!