A pin-hole cast on consists of typically very few stitches, tightly arranged around a circle. There is either no hole in the centre, or one small enough for a pin. It has a number of uses, mainly when starting small, working in the round from the centre out. You might use it to start a top down hat, or for an afghan worked from the centre.
There are many different methods to make a pin-hole cast on. For me, the easiest is to use a crochet variant of the magic loop; the method I describe here. If crochet is not your thing, and you do not currently, nor ever want to, own a hook, then do not fear! This cast on can also be worked with knitting needles. Suzanne Bryan neatly demonstrates this technique in this youtube video.
Step 1
Wrap the yarn clockwise around your finger, with the working yarn across your palm, and the tail held between finger and thumb.Step 2
Push the crochet hook through the wrap on your finger. Pick up a loop and draw it through the finger wrap.Step 3
Move the crochet hook over the finger wrap and pick up another loop. Pull this through the loop on the crochet hook. One stitch cast on.Step 4
Push the crochet hook under the finger wrap again. Pick up a loop and draw it through the finger wrap.Step 5
Move the crochet hook over the finger wrap and pick up another loop. Pull this through the first loop on the crochet hook. Another stitch cast on.Step 6
Repeat steps 4 and 5 until you have the desired number of stitches on the crochet hook. Transfer the stitches to a knitting needle. You can tighten the pin-hole cast on and reduce the hole in the centre by pulling on the tail end of the yarn.
Here you can see the pin-hole cast on worked in a small sample swatch. The swatch is worked in DK yarn on 4mm needles. The cast-on is worked in green at the centre.