Here's some sprockets that you can use with some #3 ball chain to make rudder linkages. I had previously posted some sprockets that used lamp chain, but I found out that sizes varied greatly depending where and when you bought the chain. These new sprockets use #3 ball chain, which will be consistent from vendor to vendor. What is #3 ball chain? Well if you have dog tags, they probably came with #3 ball chain. Stainless steel #3 ball chain has a tensile strength of 25 pounds.
There are 2 sizes of sprocket for the rudder side (14 and 20 teeth), and 3 sizes (24, 26, & 30 teeth) for the servo side. The standard rudder sprockets use a 4-40 nut sized for a 1/4" wrench to hold the set screw. The rudder sprockets marked "small nut" use a smaller 4-40 nut that is sized for a 3/16" wrench. The servo side sprockets were made to be used with specific standard servo wheels, but there are multiple holes drilled so they can be used with any brand or size servo.
There is an idler sprocket that can be used to connect dual rudder setups. Additionally there are rudder posts of various lengths. These are just posts that you can drill out for 1/8" ID brass tube and use to set the rudder in the ship.
Top left - rudder posts. Right side - example of two different ways to attach the servo sprocket to servo wheels/arms.
Reverse side showing the mounting of the servo wheel/arms. Two small screws are used to attach the pieces. I think the size I used was 0 x 3/16".