T-shaped pins are perhaps the most heavy duty pin style used in dressmaking, You will rarely need to use t-shaped pins with day to day sewing project, but every once in a while they do come in handy.
Compared to conventional pins used in apparel sewing, such as ball head or flat head pins, T-shaped pins are thicker and longer featuring T-shaped end on the opposite end of the needle point. This unique shape renders these pins incredibly safe and comfortable to work with and quite visible in the seam alignment process. Given that they are quite heavy duty, T-shaped pins should not be used lightweight fabric and even mediumweight ones as they may damage the fabric or leave a permanent perforation mark. On the other hand, some fabrics are difficult to align and pin without some help from T-shaped pins.
When pinning through high-pile fabrics, T-shaped pins are not only stable but very visible and comfortable to insert and remove in the sewing process. T-shaped pins are also thick and sturdy enough to pin through thicker home décor fabrics, and other heavy duty materials like burlap, canvas, a thick textured wools. While these pins are not an absolute requirement for apparel sewing, they do come in handy if you plan on expanding into heavier duty crafts and home decor.