minecraft_lzstools/data/lzstools/predicate/wrench/mainhand.json

{
  "condition": "minecraft:any_of",
  "terms": [
    {
      "condition": "minecraft:entity_properties",
      "entity": "this",
      "predicate": {
        "equipment": {
          "mainhand": {
            "predicates": {
              "minecraft:custom_data": "{lzstools:wrench}"
            }
          }
        }
      }
    }  
  ]
}