There are a few tips to ensure you do not overtighten black pipe fittings:

Use a torque wrench.

A torque wrench is designed to securely tighten fittings to a specific torque specification. This helps prevent overtightening and can ensure fittings are tightened properly. Most black pipe fittings recommend hand-tightening plus 3/4 to 1 1/2 turns using a torque wrench.

Tighten by hand first.

Always hand-tighten black pipe fittings before using a wrench. This allows the threads to start engaging evenly. Then you can use a wrench to tighten to the proper torque. Hand-tightening first will help prevent cross-threading the fitting.

Tighten in multiple passes.

Do not tighten black pipe fittings in one quick motion. Instead, tighten a bit at a time, checking your torque each time. This allows you to gradually tighten to the proper specification without overtightening. Tightening in stages is easier to control.

Consider the pipe size.

Be extra careful not to overtighten larger black pipe sizes. Larger pipe diameters require significantly more torque to tighten properly, so overtightening is more likely. Carefully follow the specified torque values for the pipe size you are connecting.

Apply joint compound.

Applying pipe joint compound to the threads can help lubricate them and make it easier to tighten fittings properly. This can reduce friction and make it less likely that you will use excess torque by accident. The lubrication also helps ensure there is a better seal created between the pipe and fitting.

Double check by re-tightening.

After tightening a fitting, take a step back and re-tighten it again with your torque wrench. This second pass helps ensure the fitting is tightened properly without being overtightened on the first try. The re-tightened fitting should still meet the recommended torque specifications.

Inspect and test the joint.

Carefully inspect the joint you have created to ensure there are no visible signs of damage or deformation from overtightening before putting the system into use. Conducting leak and pressure tests also provide a final check to validate the joint is functional and secure before hideing the pipe.

By following these tips, you can help ensure all your black pipe fittings are tightened properly without overtightening the joints. Paying close attention to torque specifications for each size of pipe will give you the most control and help avoid damage. With some practice, tightening black pipe fittings to the right specifications will become second nature.