Freewheel or Cassette

OK. Apologies if this is covered, i utfs but couldn't see anything.

Very new to actually trying to do my own bike fixing and minor alterations, having previously just let (made) Edmundro do it in exchange for beer. However - time to make a start and dip my toe in to the water.

I am 99% convinced I need to buy a new cassette rather than a freewheel, having Sheldon'd myself up - I can see splines, there is a slight bulge at the end of the hub, and the hub is a Shimano 105 (FH-1055, which I assume stands for Freehub-1055) which would make sense age wise according to Sheldon.

Is anyone able to tell from these very low quality pictures, before I spend the cash, if I have come to the right conclusion?
Thanks!

Cassette.

Next.....

Well that was easy. Thank you!

Gis a shout if you need to borrow the removal tool.

Thanks - may well take you up on that. Much more fun than letting someone else do it.

Any other 7 speed cassette will do as long as it's Shimano compatible right? The spacing is confusing me so I'm not going to try and cram any more on there.

Any 7-speed cassette should do. SRAM tend to be lighter. Can't speak for durability as I haven't worn one yet. Shimano is fine; somewhere has HG50 blocks for cheap-ish at the mo, but I can't remember who.

Thanks Rodabod. I went for the HG50 in the end so good to know the hunting and reading paid off. Hopefully it will arrive soon so I can get cracking with trying to get the last one off.