yes.
or you can just cut/sand a small part to make a square hole that the card notch can sit in. extra 30 secs of work per notch.
if or you're like me and don't touch working rigs, leave it as it is.
I put 6 monster R9 cards, still stable AF. and cheap too. later I take pic

and compared to my metal mining rig, round is a good thing. I don't have the luxury of having same cards. some have exhaust exit heat holes that will get covered by the square metal joints. some won't properly sit on the joint because of the DVI/VGA port will kacau. and some just too pendek. with round joints, there will always be space for the exit hole for any card, and any card punya notch can sit on the pipe. with metal, ako kena drill. salah drill, dah buruk. with pipes, potong is easy. salah measurement, just potong baru, it's so cheap.
if you are really anal about the pipe strength, put dirt in the pipe. a bit heavy, but strong AF.
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just need to make sure that you have room for the riser cables to cucuk, that's all.

Not really noticeable, but one side is shorter because I have a few short cards and it won't sit on it. no mining rig can accommodate this without cable ties. with pipes it's easy, just pendekkan a bit and you're done.

for beginners like me, cut panjang sikit with a small saw (30 secs per cut of work), and adjust later. once adjusted, duplicate for other pipes.
3 meter pvc pipe per rig. 5 meters if you wanna add extra stuff like fan holders.