What is the weight holding capacity for malleable iron couplings and other configurations?

We cannot provide the maximum weight bearing data for the malleable iron pipe fittings. Malleable iron couplings in either Class 150 or 300, and all other fitting configurations of M.I. pipe fittings for that matter, are not designed for, nor recommended for, load bearing applications such as a pump column.

We recommend that a steel well coupling be used to support the weight of the pump column. Steel fittings will have a much higher hoop strength. Above the coupling you can install a short pipe nipple and then one can add a M.I. tee or elbow as required to change direction, provided the operating pressure and temperature is within the allowable range.

https://support.boshart.com/what-are-the-pressure-ratings-for-class-150-and-class-300-malleable-fittings

This ensures the M.I. fitting thread is not holding the weight of the pipe column.