Ok, so Im building some hojo undo gear and looking at how karate does supplementary training like toughening the fingers, arms, hands etc. I have a similar practice in kung fu called iron palm, which involves striking a bag full of beans or gravel (depending on the users preference) for toughening the palms in a similar manner, however, I was wondering about Dit Dar Jow. My sifu who taught me qigong encourages the use of dit dar for any hand conditioning you will do, however I've yet to see anything from my time reading up on or watching that sort of body conditioning in karate. Is it truly necessary or is it something I could potentially skip?
Why would it be necessary? You're hand will still likely break if you hit someone on the temple. Just hit the bag like a regular person
I wouldnt do anything like that, unless i was taught in person by a qualified teacher. If you want SandC work, go running/swimming, swing a kettlebell or lift a barbell.