ETS-Lindgren 3148B Log Periodic Dipole Array - Manual (Page 16)

16 | Mounting Instructions
Do not cross thread or permanent damage to the adapter and
thread insert could occur.
3. Remove the mounting knob from the mounting bracket on the antenna.
4. Slide the mounting bracket onto the polarizing adapter with the
polarizing adapter placed between the shoulders of the mounting
bracket.
5. Thread the mounting knob through the mounting bracket, then through
the polarizing adapter, and finally through the hex nut.
6. Tighten the mounting knob to secure the antenna.