I am not well versed in Koken so thank-you for sharing that info. I learned something new.
That set I pictured is #4227M and the catalog confirms your wisdom of hand use only. Very interesting option.
I think, that where KoKen are concerned, there is always a risk of confusion, if only because they offer such a huge range.
Best thing to do is refer to the original catalogue, but even then, care is needed.
Basically, KoKen offer ”regular” bit sockets for hand use - No 3010. These are a two piece design, and I really like them. Replacement inserts are readily available. I have loads in both 3/8” and 1/2” drive.
As lu787a points out, they also offer an industrial finish line - No 3012 - but still for hand use. These are a one piece design, so if you prefer that you have to go “industrial finish”.
I’m not sure why you would opt for the one piece bits, but a friend who has some is of the opinion that they are incredibly tough. That seems counter intuitive, but that seems to be the way with the Hazet one piece as well, so it could be.
I would love to see some testing on this. Nothing exotic - simply a comparison of force to twist / break the different styles (and makes) of bits.
Note that they offer a very short (one inch overall) bit socket in the industrial finish.
If you go down the impact route then all the tools are black oxide (as standard) but now you have a choice of one piece or two piece.
Part number for the one piece is 13012. Note that these are very similar to the tools above, (although the metallurgy will be different) but they have the hole so can be locked on to the tool.
The two piece impacts are 13134, and would probably be my choice.
There are a huge variety of replacement bits available - hex, ball hex, Torx, pretty much everything. And of course a variety of lengths too.
