What I have found in the stress of travel, scheduling, remembering every little thing, ticket, license, wallet, guns out of the carry on, etc. is that I tend to forget where the key is. Panic ensues at the ticket counter.
I switched over to combination locks which serves two purposes. You can't lose the key, and the TSA fucks cannot ask for your key and fuck with your shit without you being present. Giving them the combo is a no-no.
Sesamee locks are much higher quality than Master, sold on Amazon. Find one with the correct sized shackle to fit your case. Pelican should be able to tell you the correct dimensions.
The simpler brass cased locks should work, like the K436 or K437. The shackle dimension is the depth and you need a depth that will keep the case closed. The black cased locks have a huge diameter loop and probably won't fit in the hole.
Here is what to avoid: