At some point everyone who's is serious about lifting will run into the problem of not being able to find a dumbbell heavy enough for one arm rows. A lot of gyms only carry up to around 130 lb. dumbbells. Some get as high as 200. But unless you're at a legit black iron gym you probably won't even find that. Of course, at homemade strength our gym is our garage, or living room, or backyard. Very few people want a rack of dumbbells in their home.
They take up way too much space. One solution is adjustable dumbbells. These are notoriously small. You can fit about 80 lbs. on them, and that's assuming you use 25 lb. plates too. This makes them too large in diameter, but still usable. One solution, albeit not the perfect one, is the "Big Ass Dumbbell". No, I'm not talking about a circus dumbbell that is large in diameter. I'm talking about the design that Matt Kroc came up with. Perhaps you have heard of Kroc rows. These utilize what is more accurately called a "long ass dumbbell". But that doesn't sound as good, nor does it produce as nice an acronym. You can buy these Kroc row bars for a few hundred dollars if you wish, or you could make them yourself. I based my design on the initial description I heard Kroc give in an interview.
The backbone of this thing is a 1 inch threaded rod. You can find threaded rods in any home improvement store, but not every store has them as large as 1 inch. I'm not sure if Home Depot or Lowes in your area will have them. I got mine at a Midwest store called Menards. They also have them at places like TSC. You'll also need 4 nuts that match your threaded rod. Then you'll need about a 6 inch length of pipe that fits over the rod. The pipe should also be called "1 inch" because pipe is measured by inner diameter and the rod by outer diameter. Of course the best way to make this all work is to just buy all the materials at one store so you can test fit them before you buy.
This project really couldn't be much more simple. you decide how big you want your dumbbell to be and cut your threaded rod to that length. The longer your rod, the more cumbersome it becomes. No matter what, you're going to end up with a dumbbell that needs to be lifted in a slightly different way, because it's simply too long to row in the conventional fashion. It utilizes standard plates (which means they have a one inch hole in the center, as opposed to olympic plates which have a 2 inch hole). If you leave it at 36 inches in length you can cram on enough 5 lb. plates to make it over 200 lbs. This will be of similar diameter to a normal dumbbell. If you use 10 lb. plates you can get it over 300 lbs. This will be slightly large in diameter, but not very much. If you cut it down it wll obviously hold less weight and you'll have to do the math yourself to figure out just how much less.
Then all you do is slide the pipe over the rod and center it. Screw a nut on each side of the pipe. Your dumbbell is basically done at that point. Load it up with plates and screw a nut on each side again to lock them down. Here's a few extra tips:
You can get 1 inch spring collar clips. These fit perfectly in the threads of your rod so they will be secure even if you hold the dumbbell in a vertical orientation. Just make sure you have a few inches of rod at each end. You don't want to load it up to maximum capacity and have a spring clip at the very edge of the rod. In those cases, lock it down with a nut. But if you aren't loading it up that much it's a pain to screw the nut on and off. In these cases it's nice to quickly use the spring clips instead.
If you lock down the two center nuts tightly your handle in the middle won't rotate. If you want it to rotate, simply loosen the two center nuts a tad until it does. In general you do want a dumbbell handle to rotate for the same reason you want a barbell to rotate. If it needs too it will simply spin rather than try to roll out of your hand.
Because of its size, you have to take a different stance when rowing this thing. First, you need the foot that's on the ground to be a bit further away from the bench. And you need to grip it slightly off center, away from your feet. This is because you need it to be higher towards your head, and lower towards your legs. This thing is so long it will literally be between your legs when you row it. As such you need to be able to touch it to your chest without jacking yourself in the crotch on every rep. This is common sense and mere trial and error will teach you how to use this thing on the first set. Or just watch videos online of people doing "Kroc Rows" if you want to prepare ahead of time.
And that's pretty much it for this project.