user
Instruction
Answer the question based on the provided table.


Table
Table Title: List of thread standards
Table Content:
| Thread\nnominal size | Outer diameter\n[mm (in)] | Threads per inch\n(TPI) | Pitch\n[in (mm)] | Inner diameter\n[mm (in)] | Cable diameter\n[mm (in)] |
| --- | --- | --- | --- | --- | --- |
| PG7 | 12.5 (0.492) | 20 | 0.05 (1.270) | 11.28 (0.444) | 3 to 6.5 (0.118 to 0.256) |
| PG9 | 15.5 (0.610) | 18 | 0.05556 (1.4112) | 13.86 (0.546) | 4 to 8 (0.157 to 0.315) |
| PG11 | 18.6 (0.732) | 18 | 0.05556 (1.4112) | 17.26 (0.680) | 5 to 10 (0.197 to 0.394) |
| PG13.5 | 20.4 (0.803) | 18 | 0.05556 (1.4112) | 19.06 (0.750) | 6 to 12 (0.236 to 0.472) |
| PG16 | 22.5 (0.886) | 18 | 0.05556 (1.4112) | 21.16 (0.833) | 10 to 14 (0.394 to 0.551) |
| PG21 | 28.3 (1.114) | 16 | 0.0625 (1.5875) | 26.78 (1.054) | 13 to 18 (0.512 to 0.709) |
| PG29 | 37.0 (1.457) | 16 | 0.0625 (1.5875) | 35.48 (1.397) | 18 to 25 (0.709 to 0.984) |
| PG36 | 47.0 (1.850) | 16 | 0.0625 (1.5875) | 45.48 (1.791) |  |
| PG42 | 54.0 (2.126) | 16 | 0.0625 (1.5875) | 52.48 (2.066) |  |
| PG48 | 59.3 (2.335) | 16 | 0.0625 (1.5875) | 57.78 (2.275) |  |


Question
what is the only thread nominal size with a 21.16mm inner diameter?


Answer Format
The final answer should be concise and use the following format:
```json
{
    "answer": [
        "answer1",
        "answer2",
        ...
    ]
}
```
rule
["PG16"]