We frequently get requests for advice regarding the correct proceedure for making fountain pen sections for Bock nib housings, particularly regarding size 5 nibs, which appear to give more trouble than the size 6 ones.

• Standard practice when establishing the correct drill size for thread taps is to subtract the pitch from the diameter. In the case of a Bock size 5 housing, that would work out as 6.4 – 0.6 = 5.8However, the very bottom of the housing has a tiny non-threaded area which has a diameter greater than the drill size.  Therefore we recommend that you use a 6mm drill, which will allow the housing to be inserted easily, without compromising the integrity of the section thread.
• Ensure that the non-threaded part of your section is marginally longer than the non- threaded part of the housing. This will allow the housing to locate on the tiny rim under the nib, and not locate by running out of thread, which could cause it to seize up. 
• Run your taps through the thread as far as possible, right to the end of the cutters, to open up the minor diameter of you section thread as much as possible. Once you have cut your thread, run a tap in as far as possible by hand from the opposite end, which will also serve to open the minor and to clear any swarf or other detritus.

Bock size 5 fountain pen nibs