A hole plate is a hole plate. The differences are in the details, not how they generate divisions.
You say you have a 90::1 worm. Then, any table for a 90::1 rotary table or dividing head will give you the numbers you need.
What to be careful about? First, you may need to alter the center hole in the plates to match the diameter of the boss on your RT. It is reasonable to assume that the existing holes are concentric with the hole circles. So when setting up (on a lathe?) to enlarge the holes, you can use the existing holes to center the disks.
As for the numbers you need in the hole circles, dividing a circle with a worm gear is all about prime numbers. If you want X equal divisions, then you need to have ALL the prime numbers in X either in your worm gear or in the hole circle. So for 48 divisions, 48 = 2 x 2 x 2 x 2 x 3. Those are the prime factors of 48. A 90::1 worm has prime factors of 2 x 3 x 3 x 5. So you have two of the prime factors of 48, a 2 and a 3. You need three more 2s in the hole circle. 2 x 2 x 2 = 8. Any multiple of 8 holes will work: 8, 16, 24, 32, etc. All of them will work to get 48 divisions with a 90::1 worm.
Generally speaking, the sets of plates with hole circles are designed to provide the additional prime numbers that are needed to generate as many even divisions as possible. They usually do so for all or most numbers under 50 and for most numbers under 100. This means that, in order to have all possible divisions under 50, the set of hole circles must have all the prime numbers under 50 that are not in the worm's ratio. That goes for any worm ratio. But just adding the missing primes is not enough as some primes are needed more than one time as shown in my example for 48 divisions above.
The 40::1 worms and 90::1 worms have different sets of prime numbers (40 = 2 x 2 x 2 x 5 while 90 = 2 x 3 x 3 x 5). So different numbers of additional primes may be needed for any particular number of divisions. Also it is normal practice to combine two or more prime numbers in a given hole circle. As an example of this, no one makes a 3 hole circle. Instead numbers like 15, 18, 21, 24, 27, etc. are used to give additional extra primes with a single hole circle. What this means is that the exact set of hole circles used with a 40::1 worm will not be the same as the set used with a 90::1 worm. If you wish to get the maximum number of divisions from a set of hole plates, then you should look for a set that was optimized for the same worm ratio that you have.
One last thing: if you have an accurate dividing head or RT, you can generate hole circles of any number of divisions with a fairly simple, but time intensive procedure. These locally generated hole circles will be just as accurate as the worm gear used to generate them. I have described this procedure a number of times. Here are links to such descriptions:
OT Rotab indexing -
The Home Shop Machinist & Machinist's Workshop Magazine's BBS
and with more details
On Dividing Heads, and how they can improve plates -
The Home Shop Machinist & Machinist's Workshop Magazine's BBS
off shore producers of dividing plates sold as accessories. You get a "kit" of parts with the plates, sector fingers and crank/indexing pin handle. Depending on the table you already have, then it all should be able to be modified to work without too much effort. Vertex and I believe Soba sell them. Vertex, Dividing Plate for Horizontal and Vertical Rotary Table, DP-3, 1001-032 : Amazon.ca: Tools & Home Improvement But as EPAIII said in his very well explained post, the worm/wheel ratio has to be exactly the same so I'd check to be certain before buying. I do know my Vertex is 90-1. Soba is in my opinion a step down in overall quality and accuracy, so this isn't something I'd be buying at the cheapest possible price. Vertex are at best ok I guess, but there sure not a Moore or Walter, so there claims of accuracy on there R/T's don't stand up on dimensions I can at least measure for allowable table flatness and Morse Taper run out. That leads me to be real suspicious about the same claims for there worm/wheel precision as well. Either way the plates and rest of the kit should still be good enough for what your wanting.
