They remind me of the devices used in CRT TV sets to drive the tube degausing coil. Two varistors, one positive temp coefficient, the other negative coefficient. When cold, current sent to the coil. On warming up (from the current passing through them) the coil current reduces smoothly to nothing.
Point being, they were constructed as two disks of material held by spring pressure between three metal plates.
The things in the picture look like there are rectangular plates of some material, held in a stack of alternating metal and active material. Looks like they rely on the shrink-plastic to apply the pressure. And the metal layers are thick, to absorb transient thermal energy? Also to keep the pressure even across the surfaces.
I also see one and probably two of them have one terminal connected to chassis ground.
Given that it's a 24V DC transient protector: two slo-blow fuses, would be on the DC plus and minus rails. There are three mystery components, so they'd be arranged as two DC rail to ground protections, and one differential (between Plus and Minus.)
I'm guessing they are MOVs, done with a stack of thin MOV compound, stacked between thick metal contacts for better energy pulse survivability, and maybe also to get the right breakdown threshold.
Their job would be to clip transients, for long enough to blow the fuses.