In a simple overview, imagine a thick-walled steel tube, about ¾ of an inch in diameter, in your left hand. One end of the tube has two flats machined into it. Now imagine a second shaft in your right hand, this one with a female socket end machined to accept the flattened end of the first shaft. The two shafts mate, but the clearances between the flats on the first shaft and the matching female socket's flats are loose. Put together, you can easily rotate the two shafts independently of each other a little bit because of the sloppy fit. But after about 15 degrees of free rotation the flats come together and the two shafts go solid.
OK, now we add a torsion bar to our mental assembly. The "T-bar," as the chassis engineers always call it, is a solid metal rod about the size of a pencil. It's firmly fixed to the shaft in your right hand, the one with the female socket. When the two shafts are slipped together, the T-bar slides through the hollow center of the other shaft, the one in your left hand with flats on the end. Once the two shafts are mated, a hefty dowel pin is driven through the shaft in your left hand and the end of the T-bar. This joins the T-bar to both shafts, and you can no longer easily rotate the two shafts independently of each other; the slop is gone.
But, as you've guessed, the T-bar is really a spring. Put enough leverage on the shaft in your left hand and it will still move relative to the second shaft, at least until the flats come in contact and the assembly goes solid.
If you've ever tried to coast your Mustang down a twisty road with the engine shut off, you've noticed how the steering feels--besides needing high effort, strangely gummy. You grunt the steering wheel a few degrees and nothing happens. Then all of a sudden the car turns and the effort drops sharply. Try to steer in the opposite direction and you go through the same sensation of winding a gigantic rubber band--that's the T-bar twisting followed by the flats finally going solid.

Now the collar has been slid...

Now the collar has been slid over the shaft assembly to form the spool valve. To the bare hands the assembly is rigid, but a steering wheel gives the leverage to twist the T-bar and vary the orifices inside the spool valve.

Here we've slid the input...

Here we've slid the input and pinion shafts together and are playing with the loose fit between them. Without the T-bar pinned to the input shaft, the two shafts have a sloppy fit before the machined flats come into contact with each other. Once the T-bar is pinned in place, you have to twist the T-bar to get any relative motion between the two shafts.

In Ford-speak, these are steering...

In Ford-speak, these are steering shafts. The short lower unit is from a Fox; the upper assembly is from an SN-95. The steering wheel end is at left, the rag joint is at right, and the universal joint that allows the steering to bend around the exhaust system is in the middle, more or less.
So, we've got our two shafts mated and pinned together via the T-bar. Now we'll add the final piece, a collar that slips over our shaft assembly. The collar is intricately machined and, among many features, has a shoulder in it that butts against the female socket on the shaft in your right hand. A dowel pin fixes the collar to that same shaft in your right hand so the collar is really part of that shaft.
Now, the collar has no locating function: It doesn't lock the two shafts together or anything like that. Its job is to form a valve in conjunction with the shaft in your left hand. Remember, the collar is pinned to the right shaft, but forms a valve with the left shaft.
The valve is formed by machining troughs into the ID of the collar and the OD of the shaft. Power steering fluid is pumped to this area and flows between the shaft and collar. As the two shafts rotate independently of each other--in the "slop" that's dampened by the T-bar--the area open to the power steering fluid changes as the shaft and collar rotate independently of each other. This ports, or controls, the amount of power steering fluid, and thus, the amount of steering assist.
And for the record, the shaft in your left hand is the steering rack assembly's input shaft; the shaft in your right hand is actually the pinion. At its other end, the right shaft is milled with gears that mate with the steering rack.

Down at the rag joint or steering...

Down at the rag joint or steering rack end of the steering shafts we see the splines on the Fox unit and the triangle of flats on the SN-95 piece. These mate with the steering rack assembly's input shaft. This joint is the one bolt-in gotcha of swapping an SN-95 rack into a Fox. Maximum Motorsports offers the necessary steering shaft combinations to make the swap, however.

And here's such a shaft--a...

And here's such a shaft--a short Fox-style steering shaft with an SN-95 end to mate with an SN-95 steering rack. These are OEM-quality (or better) shafts Maximum has welded together in critical areas to ensure they cannot come apart or loosen up. The universal joint design deletes the rag joint for greater precision and header clearance (reason enough to install this shaft in many hot rods). Retail on this part is $239.97.

And here's such a shaft--a...

And here's such a shaft--a short Fox-style steering shaft with an SN-95 end to mate with an SN-95 steering rack. These are OEM-quality (or better) shafts Maximum has welded together in critical areas to ensure they cannot come apart or loosen up. The universal joint design deletes the rag joint for greater precision and header clearance (reason enough to install this shaft in many hot rods). Retail on this part is $239.97.

Maximum Motorsports recommends...

Maximum Motorsports recommends a manual steering rack to Fox drag racers, mainly to save weight. By deleting the power steering pump, bracket, hoses, fluid, and belt, 16.15 pounds is saved according to Maximum's scale. We'll note you also save the weight of the spool valve, plus gain some steering feel because the power steering is always over-boosted when running skinny front tires. As the photo shows, the manual Flaming River steering rack assembly Maximum offers is dead simple because there is no spool valve.

If you've ever wondered why...

If you've ever wondered why you can never beat the pros, here's a little glimpse at a trade secret. This '00 Cobra R steering rack--pure unobtanium and supposedly the best-feeling, best-steering Fox/SN-95 rack of them all--is under one of Maximum Motorsport's in-house track and race cars. We're not saying this makes the Maximum car unbeatable, but it's just another one of those little things that makes the Maximum driver not have to work so hard. Also visible are Maximum's offset rack bushings.

Mustang tie rods thread onto...

Mustang tie rods thread onto the ends of the steering rack. These "inner tie-rod ends" spherical bearings are a wear point and are often worn out on the typical older Fox or SN-95. If your steering is wandering or initially feels loose when changing directions, the inner tie-rod ends are prime suspects.