T-shirts are a staple in wardrobes from mud-pie-making youngsters to designer-minded adults. No matter how varied the design, all T-shirts are made from knit fabric. The knit may be single or double knit, humble cotton or high-end jersey, but the stretch inherent in all knit fabric lends an accommodating, comfortable fit to the wearer. T-shirt hems can suffer from broken or loosened seam threads that result in an uneven, sagging hem with the unfinished edge exposed. You can repair or alter T-shirt hems on a sewing machine. You can also hem a T-shirt by hand, but a sewing machine creates more stable, small, even and attractive stitches.

Insert the ballpoint sewing machine needle into the sewing machine. Thread the machine with thread.

Position the machine's stitch length to a moderately long setting. For instance, if your machine's stitch choices go from 1 to 5 -- 5 being the longest -- 3 would be an appropriate length. Should your machine provide a zigzag option, set it at narrow; this will provide a slight zigzag shape to the stitches that allows for future material stretching with lessened risk of further hem-thread breakage.

Cut any loose or broken hemming threads from the T-shirt's hem. Pin the hem with ballpoint straight pins in the desired position. For a clean-finished hem, the raw fabric edge will be folded over twice so that it is hidden, and it will be secured in place by the stitching line.

Sew the new hem in place. Do not stretch the fabric while sewing; gently guide the knit through the presser foot, allowing the machine to do most of the fabric feeding. Trim any loose threads.

Iron the repaired hem with an iron on the appropriate setting for the T-shirt fabric. Check for any missed sections of frayed hem.

Measure and mark with a fabric marker the desired shortened T-shirt length. Remember to provide length for the hem. For a rolled or clean-finished hem edge, leaving 1 inch is adequate for turning the edge under twice, sewing 1/2 inch from the finished edge. Cut along the marked line.

For a clean-finished hem, follow Steps 1 through 5 in Section 1.

For a lighter-finished altered hem -- especially attractive for extremely lightweight knits -- finish the newly cut edge by pinking it with pinking shears. Turn the fabric up on the wrong side of the T-shirt allowing an allowance for the hem. If you plan on a 1/2-inch hem allowance, fold in the fabric by 1/2 inch and pin in place.

Stitch just below the pinked edge using a moderately long, slight zigzag stitch. Be careful not to stretch the fabric as it feeds through the presser foot. The single fold of this hem option results in less bulk than the clean-finished method.

Lightly iron the new hem with an iron set on the appropriate fabric setting. Check the altered T-shirt for fit, adjusting the new hem as needed.