In C#, when I insert a record into Access tabel, why will it cause error if the length of string

I define a field "myField" in the tabel "AccessTable", the length of "myField" is 3
when I insert a string with the length 7, it will cause error, why?

myCommand.CommandText="Insert into AccessTable (myField) values ('123457')"; //cause error!!!
myCommand.CommandText="Insert into AccessTable (myField) values ('12')"; //OK

When I do the same thing using Pascal in Delphi, if the length of string exceed the length of a field,
it will not cause error, the exceeded string will be trim automatically!

OleDbConnection myOleDbConnection=null;
OleDbTransaction trans=null;
myTreePar.myTreeView.BeginUpdate();
try
{

myOleDbConnection=ConstClass.GetDatabaseConnect();
myOleDbConnection.Open();

trans=myOleDbConnection.BeginTransaction();

OleDbCommand myCommand=new OleDbCommand();
myCommand.Connection=myOleDbConnection;
myCommand.Transaction=trans;
myCommand.CommandText="Insert into AccessTable (myField) values ('123457')";
myCommand.ExecuteNonQuery();

trans.Commit();

}
catch(Exception e)
{
MessageBox.Show(e.Message);
trans.Rollback();
}
finally
{
myOleDbConnection.Close();
}

[1257 byte] By [CUIWEI] at [2007-12-16]