Understanding the Initial Selection of the Radio Button for thymeleaf

The following is written in thymeleaf, but the initial value is not selected.

<input type="radio"th:value="${item.id}"th:field="*{selectId}"checked/>

The problem seems to be using th:field (it is initially selected when th:field is removed), but if th:field is removed, the form does not have a value and cannot pass the radio button value to the server side.

What should I write in this case?