This is a loom I designed inspired by a model by user equiFX on Thingiverse.  The posts on the model is printed separately to make them stronger.  They can be gently hammered into place with a small hammer.  The posts have a small skirt to prevent them from being hammered through the loom.   The posts can be printed in different colors, so that you can keep track of your stitches if you do more complex knits.

The posts should be printed on their sides so that the layer lines run up and down the post for maximum strength.  I also uploaded a separate model with a test pocket, so that you can test the clearances before committing to printing the entire loom.