Ordering the Correct Size Rosary Parts
Most parts suppliers will refer to "milimeters" when indicating the size of beads, eyepins, jump rings etc. Become familiar with the conversion of inches to milimeters (mm) so that your "mind's eye" can see how large a part will be.

Eyepins
Choose the right size eye pin for your bead or you'll be struggling your way through making things fit.
The larger the bead, the larger the eye pin. Too large eye pins may be trimmed with wire cutters or the cutter on your rosary pliers, but may result in uneven sizes and slows your progress. If you'll be making your own eye pins, cut all wires to the same size before begining your rosary.
Bead Sizes: Inches to Milimeters per 16" stand
Most bead vendors will offer strands of beads in 16, 20 and 24" lengths - the most economical way to purchase beads
Rosary Bracelets and Length of Rosary
Refer to chart for figuring the finished size of rosary bracelets and/or how many beads are needed of a particular size for spacers and embellishments.
Cord Rosary
Wire Gauge
Cable Chain works best for Rosaries
1 foot of chain = 34 3-link cuts
14 links needed per rosary
Measuring Crucifix and Center
What about Size of Crucifix and Center relative to bead size?
We did a little math and came up with a formula that might help if you think your Crucifix looks too small, or the center piece too large. We looked at a number of rosaries offered for sale at various sites and compared the size of the findings to the size of the bead. The most appealing, in our opinion, were the ones that had a certain proportion about them.
We found that a somewhat uniform ratio exists between all the parts: 3 to 2 to 1/2
This is no set rule, but rather a preference.
The beauty of all rosaries lies in the eye of the beholder!