Hello,
I am trying to draw a flange which is basically a circle with holes inset in the circle and evenly spaced around the circumference. The diameter of the circle is 20.625 inches. the holes are inset in the circle .75 inches and are evenly spaced around the circumference 4.25 inches apart. The holes are .375 diameter. Thanks for any help!

Create a grid with inch units, you'll probably need a quarter of an inch as the grid spacing and set major line to be every 4 lines, set the default doc units to inches as well so rulers will show inches too.

Create a circle, select it and on the Selector toolbar click the padlock to preserve the aspect ratio when changing size. Enter 20.625, this is your base circle. Align it with the grid on one side, this is the side you'll use as reference for helper circle. Snapping to grid should be On of course.

Now duplicate the circle, change it's color to something else so it's easy to tell them apart when you start to edit it. Zoom in on the side where they are aligned with the grid, select the duplicate circle if it's not already selected, hold Ctrl and Shift and click on the arrow to make the circle smaller. As you drag the circle will snap to grid, release it when you get to the third grid line, that is 0.75 of an inch from the original circle's rim.

Now create a new circle, and set it's size to 0.375 in the Selector toolbar. Position it inside the reference circle so their rims are touching, disable the grid temporarily while you're doing it if it give you problems with positioning.

With the grid disabled click on the hole circle the second time to get rotation arrows and rotation center mark. Grab the rotation mark to the center of the reference circle and snap it there (in the snapping options you should have Snap from and to rotation center enabled, this option is available in 0.47pre, if you are using 0.46 try to find another way to find the center and snap there, guides for example).

Now clone the hole circle and rotate it, it will track the reference circle's rim. I'm not sure what the 4.25 inches apart actually means, convert it to degrees and you can use Create tiled clones option to create all the holes in one go. When you've got the holes you can delete the reference circle, or just remove it's fill to make it invisible but you can select it while in Outline mode if you ever need it later.

I have another question. Why do you need it in Inkscape? You know the flange you want to draw will be just a circle with the holes.... If you try to show some system you will need some 3D...