You're probably looking for a Cane bolt similar to this: https://www.homedepot.com/p/Everbilt-12-in-Black-Gate-Cane-Bolt-15464/202042236 Other sizes are available.
My sheltie was in within 5 min, so yes, a bear could definitely break in!
Standard locks will work.
NO, do NOT expect this latch to hold anything securely!
Currently we do not carry replacement parts for the slide bolt.
These slide bolts includes the following fasteners: 2) 1/4"x2-1/2" Carriage Bolts, (2) #10×1-1/4" Pan Head Sheet Metal tapping screws, and (2) 1/4"Hex Nuts.
My garden gate is 52 inches wide so my tiller and wheelbarrow have no trouble entering. The mounting plate is around 4 inches.
I built this into a wooden gate that latches to a 4x4 post. I agree that visible (and accessible) nuts on the outside are less safe,..., so I did not use the 2 bolts that were included in the packaging. Instead I used 4 screws that were slightly smaller than the 4 square holes. It would be easier for someone to climb the gate or surrounding structure than it would be to unlatch the slide bolt.