For the retrieval of the data from textboxes you can use .FindControl() method:
foreach(DataRow row in GridView.Rows)
{
TextBox txtClearence = (textBox)row.FindControl("_txtClearence");
TextBox txtHeight = (textBox)row.FindControl("_txtHeight");
string valClearence = txtClearence.Text;
string valHeight = txtHeight.Text;
}
For insert to the database you can find an example
here[
^]
Good luck,
OI