How to add sculpt keys/joint to subtool

Hi, I’m brand new to zBrushCore but I’ve been watching tutorial videos to get the basics. There’s one thing I’ve seen in videos but I can’t seem to find any info or how-to video. I’ll use an example - I’m sculpting a humanoid figure for 3D printing. The sculpt is broken down in subtools (head, torso, arms, legs).<br>
<br>After printing, I would like to be able to connect the arms back to the torso by adding a convex cube-shaped key or joint to the arms near the shoulder and a concave cube-shaped slot in the upper torso for the arms to make the connection.<br>
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How would I go about adding the joint key to the arms while removing the same shape in the torso to provide a flush connection after printing? I’m not sure if it’s a zsphere I’d have to use or IMM. Hope I’m being clear.<br>
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Thanks.