This is a spur drive I make.   I used one of these on drive spindle and another on the live center to hold the 390 pound finial and had no problems.  The center pin is 1/2" long and the outer pins are 1/4" long.  The longer center pin is essential for perfect centering of square stock.  The outer pins are not aligned with the center pin so that the turning can be only be remounted one way.  This assures that the turning will be perfectly centered when remounted.  This version is used on flat stock but on green wood with the bark on it I use one that has 1 1/4" and 3/4" pins.    Pins are made from 3/16" cold rolled stock.  They are easy to make if you have a welder.  I fill the thread area to within 1/4" of the top with sand and drop in the largest washer that will fit.  I then fill the remaining area and slightly above the face of the nut with weld.   Nut is mounted on the lathe and using a angle grinder the face is ground slightly concave.  Using a drill chuck on the tail stock, drill appropriate size hole all the way through weld material.  Insert over length pin 1/8" shy of back side of weld and weld in place being careful not to get splatter on the threads.   Mount on lathe  at modest speed grind to desired shape and length.  Then weld pins on outside of nut.

Center I use on the head stock for turning spindles.  The pin will hold the stock and pressure from the tail stock is adjusted so the spindle will not slip under normal turning.  When you get a catch the stock will slip and you end up with less damage to the turning and you.  Also make it possible to remove and mount stock without turning off the lathe.  A handy feature when doing production spindle turning.

I turn a lot of fir dowels for a timber framer that have to be 1.26" to 1.26" in diameter.  Using a 1.25" forester bit gives me a handy reference.  Also unlike a standard spur drive it doesn't tend to split the stock.