For thumb - Keep a tail so you can fix any hole there. I did 9 rows of stockinette rather than one before doing the garter edge for thumb. Try it on to see if you need extra rows, I have long fingers. On the last row of garter edge, pull yarn through but don’t cut it until you try it on to be sure thumb is long enough.

Modifications:
When doing the increases for the thumb, do the last set of yarnover increases (before putting stitches on thread) as backward yo so less of a hole. When you start the thumb, pick up 3 sts at end the do k2tog on next round at inner thumb.

For garter border at top of hand, on second knit row k2tog k8 around to reduce 10%(5sts). That brings the top in a little around your hand so it doesn’t gap away from the hand so much. I did 8 rows of garter (3 ridges, bind off in purl) at top of hand.

The garter edge of mitts start about 3” below the crease of my wrist after blocking. They’re really beautiful, especially after blocking and they “fit like a glove” which is so wonderful.

Pre-blocking measurements:
Width: 3 1/2”
Length: 7 1/4”
Length of thumb (outside): 3”
Length of thumb (inside): 1 1/2”

After-blocking measurements:
Width: 3 1/2”
Length: 7 3/4”
Length of thumb (outside): 2 3/4”
Length of thumb (inside): 1 1/4