It must be 1-1/4" gas line. The entire house must be load calculated to see what size pipe is required between the Tee and the meter. Undersizing fuel gas pipe can have disastrous consequences. The International Fuel Gas Code specifies pipe sizes for good reason. If you are too cheap or stupid to comply with Code and thus safeguard your family and yourself, at least post the name of your community so we know where the explosion is likely to originate.
MM