minecraft-assets/assets/minecraft/blockstates/chain.json

{
  "variants": {
    "axis=x": {
      "model": "minecraft:block/chain",
      "x": 90,
      "y": 90
    },
    "axis=y": {
      "model": "minecraft:block/chain"
    },
    "axis=z": {
      "model": "minecraft:block/chain",
      "x": 90
    }
  }
}