Double Decrease: Purl 3 together
P3tog is a knitting double decrease – that means that where there were three stitches on the old needle (usually the left-hand needle), there will only be one stitch on the new needle.
For single decreases, many pattern writers will simply tell you to decrease, without specifying which one to use. But for double decreases, the pattern writers will usually tell you which specific decrease to use.
If you are working in Stocking Stitch (alternating a row of Knit with a row of Purl), this decrease would generally only be done on a Purl row. Or it could be done anywhere to provide some desired texture.
P3tog results in left-leaning stitches on the other side of the fabric.
How to do a P3tog
The P3tog is similar in concept to the P2tog.
And it is similar to the ordinary Purl stitch.
The only difference is that at the beginning of working the stitch, you insert the new needle purlwise under three stitches, not one or two.
Remember that the yarn has to be in front before starting to make this stitch.
And notice that in the photo the yarn has been positioned properly over the stitches so that it can be pulled through those three stitches to complete the Purl motion.
This is an easy double-decrease to knit.