I've been working on an app which allows you to design Turk's head knots so they can be 3D printed. Recently, I released the very first version which creates Turk's head rings. It can be found here: http://knots.freakinsweetapps.com

This instructable explains how to use the app so you can order a 3D printed Turk's head ring.

Step 1: Find Your Ring Size

If you have a ring that fits you, but don't know its size, you can go to http://findmyringsize.com. There you can place a credit card (or anything the same size as a credit card) on your screen so it knows how many pixels your screen displays per inch. Once you do that, it will display a number of circles which you can put your ring up against to see which size your ring is.

If you don't have a ring that fits, you can find your ring size by using a strip of paper. Cut a strip of paper about the width of how tall you want the ring to be. Wrap it around your finger and mark it with a pen. Then measure up to the mark and look up your size in the chart below.

inches	mm	Ring Size
1.44	36.5	0
1.46	37.2	¼
1.49	37.8	½
1.51	38.5	¾
1.54	39.1	1
1.56	39.7	1¼
1.59	40.4	1½
1.61	41	1¾
1.64	41.7	2
1.67	42.3	2¼
1.69	42.9	2½
1.72	43.6	2¾
1.74	44.2	3
1.77	44.8	3¼
1.79	45.5	3½
1.82	46.1	3¾
1.84	46.8	4
1.87	47.4	4¼
1.89	48	4½
1.92	48.7	4¾
1.94	49.3	5
1.97	50	5¼
1.99	50.6	5½
2.02	51.2	5¾
2.04	51.9	6
2.07	52.5	6¼
2.09	53.1	6½
2.12	53.8	6¾
2.14	54.4	7
2.17	55.1	7¼
2.19	55.7	7½
2.22	56.3	7¾
2.24	57	8
2.27	57.6	8¼
2.29	58.3	8½
2.32	58.9	8¾
2.34	59.5	9
2.37	60.2	9¼
2.39	60.8	9½
2.42	61.4	9¾
2.44	62.1	10
2.47	62.7	10¼
2.49	63.4	10½
2.52	64	10¾
2.54	64.6	11
2.57	65.3	11¼
2.59	65.9	11½
2.62	66.6	11¾
2.65	67.2	12
2.67	67.8	12¼
2.7	68.5	12½
2.72	69.1	12¾
2.75	69.7	13
2.77	70.4	13¼
2.8	71	13½
2.82	71.7	13¾
2.85	72.3	14
2.87	72.9	14¼
2.9	73.6	14½
2.92	74.2	14¾
2.95	74.8	15
2.97	75.5	15¼
3	76.1	15½
3.02	76.8	15¾
3.05	77.4	16

Step 2: Dial in Your Ring

Go to http://knots.freakinsweetapps.com and click 'Get Started!'. If this is your first time, you may need to install the Unity3D plugin. Once installed you should see a ring with some sliders around it. Dragging the sliders will change the ring size and height of the ring as well as the density of the weave. When you've designed the ring you like, click the 'I Want This Ring' button. The ring will be uploaded to Shapeways and when it's ready you'll be redirected to Shapeways where you can order the ring. It can take a minute or two to process your ring. In extreme cases, it can take even longer. If for some reason you leave the page before being taken to Shapeways, you can go directly to my Shapeways shop and find your ring (it will most likely be the very last one, or at least near the end): http://www.shapeways.com/shops/freakinsweetknots

Step 3: Order From Shapeways

Once redirected to Shapeways, you can select a material of your choice. You can order plastic in a number of different colors, or you can choose one of the metals which include stainless steel, silver and gold plated brass. Once you've chosen a material, click 'Buy Now'. You can then click the 'Checkout' button from your cart at the top of the page. Fill out your payment info and shipping information and you're good to go!