Penticton, British Columbia
Boat Name: Will o' The Wisp
Hull No. 8276
Hailing Port: Penticton
12/06/2005 6:44 PM Pacific Time
What size tap do I use for a hole drilled with a 5/32" drill bit? I have checked all the hardwares in my area and not one has a 5/32" tap. Am I missing something?
Boat Name: Marrakesh
Hull No. 13645
Hailing Port: Rochester, NY
12/07/2005 3:28 AM Pacific Time
Tap drills are usually usually numbered or lettered, as they are not common fractions. 5/32 is 0.156". The nearest thread sizes for this size hole are:
3/16-32 fine (#22 drill recommended = 0.157")
10-24 coarse (#25 drill recommended = 0.1495")
If you can get a screw or bolt in the 3/16-32, that would be the best fit. If the hole is driled by hand, it is probably slightly oversize.
Boat Name: Sea Sharp Minor
Model/Year: Catalina 22 - 1984 - Swing Keel
Hull No. 11823
Hailing Port: Lake Norman Sailing Club
12/07/2005 9:31 AM Pacific Time
More clearification on tap and drill sizes.
The size of bolts and the tap that makes internal threads are designated by the outside diameter of the thread. The drill used with a given tap is the size of the root of the thread or it's smallest diameter.
In the US, sizes under 1/4 inch diameter use two numbers to designate the thread, like 8-32 or 10-24. The first number designates the outside dia and the second the number of threads per inch. To convert the first number to the actual outside dia, consider a size 5 equal to 0.125 inches. Then add or subtract 0.013 inches for each size up or down. Thus a 10-24 thread has an outside diameter of .125 + 5(.013) = .190 This method is used for sizes from 2 thru 12 but the odd numbered sizes are not commonly used. Above that, the actual outside diameter is used as fractions of an inch like 1/4-20 or 3/8-16.
For most sizes there is a choice of fine or coarse threads. For example there is a 10-32 fine or a 10-24 course, a 1/4-24 fine or a 1/4-20 coarse and the drill sizes for the corresponding taps are different.
The proper drill size can be found in may books and it is usually listed on the package of the tap or the storage box of a tap set. In the case above, the tap for a hole closest to .156 is a 10-32 which uses a .159 drill.