This anti-rust steel, John James Curved Mattress/Upholstery Needles sold by the dozen.
The 24 x 1 is a 24-gauge needle measuring approx. 1" from tip to tip.
The 21 x 2 is a 21-gauge needle measuring approx. 2" from tip to tip.
The 20 x 2.5 is a 20-gauge needle measuring approx. 2 5" from tip to tip.
The 17 x 3 is a 17-gauge needle measuring approx. 3" from tip to tip.