Yea, once again the value of a metal lathe is proven! It is odd, however, that the insert didn't fit the lathe - I've never run into that using the chucks on multiple lathes with a variety of spindle thread sizes, including some with 1" spindles. (I have a couple of Jet Mini lathes and one chuck with an insert for those.) Is the insert a Nova or another brand?
I don't remember if you said the type of lathe you have. Could it be the threads on the lathe spindle are a little out of "spec"? If so, I'd be concerned that other attachments might not fit, things like face plates and collet chucks. Or you might have to repeat the machining if you get another chuck. I'll try to measure the OD of my two smaller lathes for comparison but I don't have an easy way to measure thread depth.
Unlike metal work, a little runout on a woodturning chuck is not a problem since you always turn the wood round after mounting in a chuck. Unlike metal, the nature of wood usually prevents perfectly remounting a piece after it is removed from the jaws. (The wood fibers are crushed and deformed when tightened in chuck jaws and the wood itself moves with time and humidity changes.) If you know you will remount something it helps to mark the position of the jaws on the wood and remount in the same position, trying to get the jaws in the same depressions. (I usually make a mark between the #1 and #4 jaws.) Even then perfect truing is unlikely so it may be necessary to make another light truing cut if needed.
Sometimes you HAVE to remount the piece on the lathe, perhaps when reversing the piece to turn the bottom or some other special step on an oddly-shaped piece, for example, jamming between two pieces of wood or mounting on a vacuum chuck. Most people get close by using a finger or something to judge the runout. Remounting is where I use a dial indicator on the wood lathe - so much easier! Even then if I can get a 4" diameter piece to with .003 or .004 I'm happy.
This is held by friction, jammed between two pieces of wood turned to match the concave curves on each end.
Dial_indicator_IMG_20141122.jpg
BTW, I leave most of my precision measuring things at the mill and metal lathe. To a metal worker, woodturning might sound pretty crude but it is rare to actually have to measure something closely to an actual value! However, approximate relative sizes are sometimes important - I use dividers quite a bit as well as spring ID and OD calipers. The calipers I use most often at the lathe for spindle turning are cheap and crude stamped-metal verniers. I found them once on Amazon for $4 each and keep a bunch so I can set several and different diameters when sizing something such as when duplicating a spindle or turning a small tenon. So the jaws will slip nicely over the rotating wood, it is best to round them slightly as in the first one here:
calipers.jpg
JKJ