iOS tableHeaderView have default height?

In tableView to set tableHeaderView, we found that if you set tableView.tableHeaderView = [UIView new], where highly tableView not set, but the system will default to the tableView a fixed height, a height if you want to clear out the need to tableHeaderView small height can be specified

self.tableView.tableHeaderView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, SCREEN_WIDTH, 0.01f)];