My wife bought 2 baby/pet gates for $30 from a local Lifeline charity store to control our new puppy but they kept coming away from the door frames.
I bought a new one for $49 from Kmart and we noticed that it had 4 mating receptacles for attaching to the door frames which were missing from the old ones from Lifeline.
The original receptacles may have been left glued and screwed to the door frames by the original owner/s or had got lost in subsequent handling.
I went to Bunnings hoping to find suitable replacements for the missing receptacles, and to my surprise, Bunnings stock both baby gates and some spare parts for them. I bought 2 packs of the mounting/adjusting screw assemblies, which included the missing receptacles, for $8.50 each.
The screw assemblies were white so they matched the white gates so we used the complete kits instead of reusing the original black assemblies.
Even with the cost of the 2 mounting kits, the 2 used gates cost less than the new one and we have 3 bedroom doors puppy proofed.
If you are trying to use an existing gate, make sure that it has the 4 receptacles for fitting to the door frame or get some from Bunnings.