(Measured at the large end of the holes)
The convention for specifying peg size is the diameter of the shaft at the collar of the peg, not where the peg enters the pegbox. The standard extensions from pegbox to collar after the pegs are worn in and properly seated are: violin 12mm, viola 13mm, cello 20mm. Fit the pegs about 1mm longer than this before applying peg dope and fully seating the pegs.
The 3-4 blocks (violin and cello) are the recommended size for fitting new pegs in a new instrument, or one with newly bushed holes. Viola pegs are about .5mm larger than violin and could require the 5-6 block. The largest sizes are intended for cutting bushings. The 1-2 block is for use on instruments below 1/2 size.
|Violin and Viola||Cello|
|Block Size||Hole Size||Block Size||Hole Size|
|1-2||6.30 mm, 6.65 mm||1-2||10.15 mm, 10.68 mm|
|3-4||7.01 mm, 7.36 mm||3-4||11.21 mm, 11.75 mm|
|5-6||7.72 mm, 8.07 mm||5-6||12.28 mm, 12.81 mm|
|7-8||8.43 mm, 8.78 mm||7-8||13.34 mm, 13.87 mm|
|9-10||9.14 mm, 9.49 mm||9-10||14.40 mm, 14.94 mm|
|11-12||9.85 mm, 10.20 mm||11-12||15.47 mm, 16.00 mm|