None can, afaik.
Not sure how do mod it in. Maybe look at the firebelt for a start
"type" : "ARMOR",
"id" : "fireman_belt",
"name" : "firefighter belt",
"volume" : 2,
"material_thickness" : 0,
"storage" : 4,
"covers" : ["TORSO"],
"description" : "A stout firefighter's belt. Useful for keeping your bunker gear up, it also doubles as an equipment belt with a reinforced loop for holding a large tool.",
"weight" : 210,
"color" : "yellow",
"encumbrance" : 0,
"price" : 9000,
"material" : ["leather", "steel"],
"coverage" : 0,
"symbol" : "[",
"bashing" : 5,
"flags" : ["FANCY", "WAIST", "NO_QUICKDRAW"],
"warmth" : 0,
"use_action" : {
"type": "holster",
"holster_prompt": "Attach what to belt loop?",
"holster_msg": "You clip your %s to your %s",
"max_volume": 5,
"max_weight": 3600,
"draw_cost": 50,
"flags": ["BELT_CLIP"]
^^ Nope. Try crowbar next
{
“id”: “crowbar”,
“type”: “TOOL”,
“symbol”: “;”,
“color”: “dark_gray”,
“name”: “crowbar”,
“description”: “This is a hefty prying tool. Use it to open locked doors without destroying them or to lift manhole covers. You could also wield it to bash some heads in.”,
“price”: 1300,
“material”: “steel”,
“weight”: 500,
“volume”: 4,
“bashing”: 14,
“cutting”: 1,
“to_hit”: 2,
“flags”: [“BELT_CLIP”],
“use_action”: “CROWBAR”,
"flags": ["BELT_CLIP"],
^^ here we go. That is what likely lets it be clipped at all, and the fire belt also has a useaction flag "belt_clip.
So it looks like adding that flag to any useaction_holster item with the belt_clip flag and a set volume would allow that item to be holstered. So a mod to holster a fire axe is doable?