I currently do skull crusher twice a week as well as my compound exercises like bench, incline, ohp and chin ups in a full body split
I like skull crushers as they really blow my tricep and I can feel them
But the question is, is it silly to do only skull crushers as my direct tricep work. Monday and Friday
3 sets for 6-12 twice a week in a double progression
although skull crusher are great for triceps. They can be incredibly hard on the elbow joints. I’d say once a week is enough as long as your workout body part volume is spread out appropriately.
If you’re progressing and everything feels good then there’s no major reason to stop doing it… BUT you might start to get elbow pain as the weights go up with that kind of frequency.
You may be better served long-term to do skullcrushers one day and a different tricep exercise on another day. Or with the pressing volume you’ve already got, you may not even need to directly train them twice a week.
To be honest is more a ego thing we all want massive arms lol 
which mine are not
And every time I do skull crushers my arms feel twice the size
What’s the next best tricep exercises
Best is subjective. We all have different favourites in terms of what we feel the most in the muscle and find progression most straight forward with. Personally I’ve always loved tricep pushdowns which would be a great choice as a second tricep exercise perhaps on a different day.
Depending on the rest of your program, Dips and Close-Grip Bench Press are also fantastic choices for tricep development, but as they are compound movements they need to be programmed a bit more intelligently.
I’d say something that hits the long head more as pressing doesn’t hit that as much (so i’ve read).
So maybe skull crushers one session and overhead tricep extensions the other?
Or even try laying skull crushers one day and incline skull crushers the next to ensure you don’t aggravate the elbow with the exact same movement.
pretty sure I remember ready that Larry Scott did a heap of these laying on an inclide plank of wood when he first started training maybe @RT_Nomad will remember reading it too. It worked out pretty good for Larry. As long as your elbows can take it, thern play on.
I had never heard of this being done by Larry Scott. But he sure had by far the best arms in bodybuilding by quite a bit for long after he quit competing.
IMO, skull crushers were the single best exercise that attributed to the size and fullness of my triceps, but they played a toll on my elbows and had to quit doing them in 1977. I used just too much weight for sets of 8 reps. And I did them twice a week. It was definitely my go-to triceps mass builder. Going forward, my triceps size seemed a real challenge to grow without doing skull crushers.
I think dips are huge! Get form down, start adding weight, and watch your tri’s explode.
Dips
Tricep Pushdowns
Dumbbell Seated behind neck skullcrushers
If it’s good enough for Cbum, it’s good enough for me
Close Grip Bnch
Overhead extensions
Unilateral Pulley kickbacks
Cable push downs, pronated & supinated grip. Supinated (palms up) takes some getting used to, so don’t be afraid of working in like the 15+ rep range for a while.
Doing dumbbell skullcrushers from the floor gives me an almost Skullcrusher feeling with less elbow trauma, if you find yours getting beat up.
I like rope press downs, bent over pressdowns (so my shoulder is “overhead”), close grip floor press, machine dips, close grip pushups.
If Skullcrushers and Extensions with barbells give you trouble, don’t forget about PJR Pullovers. The way the DB sits in your hands takes all the pressure off elbows and puts it in the tris.
These work best of all for my triceps, but always end up killing my elbows!
I can never move any meaningful weight with the supinated grip - any particular advantages to doing it this way? It always makes me feel like I may as well do tricep kickbacks 
I always felt like they sucked tbh. Someone will shut me down and call me an idiot I’m sure… but the way I see it is you’re just crippling the amount of weight you can use whilst allowing the wrist to become a potential limiting factor.
But that’s the great thing about lifting, we can both be wrong and both be right at the same time. People sometimes argue when completely ignoring individual nuance.
This is why the best answer is often “try it and see”.
I like to do this triple set where you take an ez-curl bar, get on a flat bench, and do a horizontal overhead press, switch to skullcrushers, and then close grip bench to failure.
Like 21s for triceps. Makes sense.
I hadn’t thought of it that way, but you’re right.
I used to do skullcrushers for 3 reps, then close grip bench for 3 reps, then skullcrushers for 3 reps. All the way up to 40 total reps.
Whether it was a good way to train, I don’t know, but the pump was insane and the close-grip bench worked as a sort of rest pause to keep repping out more skullcrushers. Never got along with skullcrushers though so never did it for an extended period of time.
JM press enters the conversation.