One of the most frequent questions I get is "where can I find the threads you use for buttonholes?". My go-to gimp is Agreman and the silk twist I usually use is R753, both products by Gutermann. It has sometimes been challenging to find it at retail, especially in the U.S., but there is now a new source over here. I haven't used them- the National Sales Manager at Gutermann is a friend and she let me know about them.
Bay Tailor Supply is now stocking these items. If someone orders from them, do let me know how the service is.
Hand Made Buttonholes from Jeffery D on Vimeo.
