From the above source but the bolding of text is mine
Your lockblade folding knife should have a thumbstud, thumb"hole", thumb "disk" or similar push-thingy, so long as the "thingy" is attached directly to the blade (versus on the grip and linked up via a gearbox of sorts). It should not have a spring that does ALL the opening (yes, the Kershaw Ken Onion series seems to be OK). And finally, the blade needs to have at least some tendency to stay closed in the pocket or whatever bias a "bias towards closure" or "detent" (discussed in more detail later in this chapter).