SELECT 
  COUNT(thread_id) 
FROM 
  cscart_cp_pow_recomends 
WHERE 
  thread_id IN (19302)

Query time 0.00030

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_cp_pow_recomends",
          "access_type": "ref",
          "possible_keys": ["thread_id"],
          "key": "thread_id",
          "key_length": "3",
          "used_key_parts": ["thread_id"],
          "ref": ["const"],
          "rows": 1,
          "filtered": 100,
          "using_index": true
        }
      }
    ]
  }
}