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I have found that many (most?) end pins seem to have a 3º taper, even though they are often said to be 5º. A standard 3º bridge pin reamer is usually too narrow to make a big enough hole for some of these end pins. I have been looking for a larger reamer but get bogged down because while the taper of the pins is usually described in degrees, many reamers, particularly for violin and cello makers, are described as "1/30" or "1/25" for example. Can anyone give me a conversion figure so I know what "fraction" equates to 3º? Thanks - Bruce W.

interesting I can't say I ever heard them called this way. I use this taper
https://www.amazon.com/JFDWOPHT-5-degre ... 111&sr=8-2

I may have goofed on this - the designation is "1:30", not "1/30". Here are some stringed instrument reamers at Southwest Strings with this type of designation:

https://www.swstrings.com/product/lutherie/other/R201

I do have an older reamer which I assumed was 5º like the one on Amazon you linked to John, but the end pins I am using do not fit in these holes; the inner end is tight but the outer end is loose. 3º seems perfect; I just need one with a larger diameter at the big end (about .331 or 8.4 mm). LMI had one that was larger but with their closing it looks like they are sold out.

the one I posted was for a 5 degree actuall. it is one I use they are not that costly and do a good job

1 in 30 or 1 in 25 is the tangent of the angle, so you want (using 1 in 25 as the example, 1/25 = 0.04):

Angle = arctan(0.04) = 2.29061 degrees

thanks for that explanation

I have found a taper calculator online that I am able to use:

https://www.easycalculation.com/shapes/ ... ulator.php

I have a reamer that I bought from Philadephia Luthier Supply as a 3º reamer. To test this site, I measured it carefully and put in the dimensions: narrow end 3.85 mm; wide end 7.86 mm; length between 77.31 mm. The calculator says the angle is 1.4856º. I am assuming (hoping) that it is measuring the angle of one side of the taper to the centre line, and that the included angle of the two sides is twice that or 2.9712º, close enough to 3º. Does that make sense? Bruce W. (who is not a math guy . . .)

Likely. I'm never sure whether they're specifying "included angle" or "angle per side." It sounds as though your 3 degree reamer is 3 degree included angle, or 1.5 degrees per side.