I am pretty sure Rick covered this, but no one posted pics...
Most of the owners here use one of two ways to mount ledges...
Either Hanger bolts, or Lag screws.
Depending on thickness of the wood being used, and the amount of weight it will support, you can choose the size and length of the bolt.
I use 1/4"-20 hanger bolts and 3/8" Lag screws to mount 1" wood, but you could use up to 3/8"-16 for 2 inch wood. I use bolts that are 2" or longer, any shorter and you risk splitting the wood from stress. To be honest any of these will support your chin jumping on them. I prefer to keep the weight as light as possible so I do not overload the cage bars. You will also notice in the picture, there are 2 types of washers. The smaller 1 1/2" that can be purchased at HomeDepot or Lowes, and the Larger 1 5/8" Washers from ACE Hardware or a nut & bolt distributor. If you own a Ferret Nation cage you will need the larger washers due to the wide vertical bar spacing. Trust me you dont want your chin to leap blindly onto a ledge that will give way and fall.
Here is a picture of all the hardware
Before you start any screw or bolt project it is important to drill "Relief Holes" or "Pilot Holes". Wood, especially hard wood can split if you try and drive a screw or bolt into it. If you drill a slightly smaller hole than the bolt, you remove the materiel making it easier for the bolt to bite into the wood. It is more time consuming, but gives a professional fit, and keeps the bolt more secure in the wood. When you pick a drill size for the fastener you are using, line up the bit with the bolt or screw, and make sure the inside of the bolt barely overshadows the drill bit (see pic). Most drill bits will drill a hole slightly larger than their stated size, due to wobble from the drill head, or bit alignment. I am using a 9/64" drill bit for the 3/8" bolts.
If you decide to use hanger bolts I will show you a trick for installing and removing them quickly without damage, and without getting the wing nut stuck (cross threading). You can use wing nuts, but the more appropriate way is to use hex nuts. First thread the 2 Hex nuts onto the bolt (see pic).
Then turn the 2 hex nuts in opposite directions until they stop against each other, turn until they are finger tight (see pic).
Next use a Socket wrench, Hex wrench, or Crescent wrench to turn the top nut only. This puts all of the torque of the wrench into turning the bolt into the wood(see pic). You can then reverse the wrench and unscrew the 2 nuts by hand.
This is a picture of a finished Hanger bolt. As you can see, it will hang out of the cage a good 3/4", but allows you to quickly remove ledges with a wing nut. You could remove the end of the bolt with a grinder, dremmel tool, or bolt cutter, but without a Tap & Die set, you risk damaging the threads of the bolt permanently.
I prefer using lag screws... They require tools to remove, but offer a clean flush fit, and do not snag clothing and door frames when moving cages.
Currently it is about the same price for both options.