I've had Tahoe in this cage:

ever since I brought him home. Its a CA Malibu model. 18 by 20, shown exactly as depicted. I thought it was completely parrotlet proof- the bar spacing is appropriate, and I couldn't find anywhere visible for him to squeeze his little head through.
Today, my mom was joking with me and looked towards Tahoe's cage and goes 'Emily I think Tahoe is missing, I don't see him.' Then she really started looking for him... and couldn't find him. He was wedged in the bottom left hand corner of the cage- head OUT of the cage. Where you put the grate in the cage, there is a gap so you can put the grate in easy. A gap above the grate, so small I can put my finger, and thats it. Tahoe was apparently digging around in the bottom of his cage, and got his head through that gap and was stuck.
We had to bend the grate to get him out. I am praising my lucky stars that our cats don't care about the birds... they could have given him a heart attack. When we found him, poor baby was almost strangling himself trying to get free.
Needless to say, we went out and bought him a new cage ASAP.
Just a warning for all plet owners. Be careful!