Only some items have a distinction by sizes. Specifically, these are rings, bangles and some other bracelets.

The sizes of Giovanni Raspini rings are given in Italian sizes:
12 (⌀ mm 16,5 – circ. mm 51,8)
13 (⌀ mm 16,8 - circ. mm 52,8)
14 (⌀ mm 17,2 - circ. mm 54,0)
15 (⌀ mm 17,4 - circ. mm 54,6)
16 (⌀ mm 17,8 - circ. mm 55,9)
17 (⌀ mm 18,1 - circ. mm 56,8)
18 (⌀ mm 18,5 - circ. mm 58,1)
19 (⌀ mm 18,8 - circ. mm 59,0) 
Some rings may show, in addition or exclusively, man sizes:
22 (⌀ mm 19,8 - circ. mm 62,2)
23 (⌀ mm 20,0 - circ. mm 62,8)
26 (⌀ mm 21,0 - circ. mm 65,9)
27 (⌀ mm 21,2 - circ. mm 66,6)
30 (⌀ mm 22,2 - circ. mm 69,7)
31 (⌀ mm 22,5 - circ. mm 70,7)
Some rings may have, in addition, smaller sizes:
10 (⌀ mm 16,0 - circ. mm 50,2)
11 (⌀ mm 16,2 - circ. mm 50,9)
If you are in possession of a ring that fits you well, measure the diameter on the inside edge and choose the relevant size; but if you want to use your finger circumference, measure this in the exact position of where you wear the ring, clutching tightly. If you are undecided between two sizes, we recommend you choose the larger one. It is possible that rings of the same size have a slightly different fit depending on their design: large rings, which tend to bind up the finger, for example, will have a smaller fit.

The sizes of bangles are instead based on their diameter. 
S (⌀ mm 60)
M (⌀ mm 65)
L (⌀ mm 70)

Some other jewels may have a distinction in size, indicating their length.
The rest of Giovanni Raspini products has instead a one size only, but very often it is possible to adjust the measure, in particular in all the cases in which the jewel has a coupling with chain mesh: in this case it will be possible to hook the lobster clasp to a more internal mesh, rather than at the end, in order to shorten a bracelet or a necklace (it is the case of those jewels that are described with "adjustable length” in their Details section). 
The lengths expressed in the product sheets related to this type of bracelets and necklaces concern, in any case, the largest wear; the length stated never includes the ends of the chain that may have a logo medallion and horn.