DaHo Hollow Threading Needles have been sized by their length so if a customer has more than one of them, they can stand them on their open end and find the one they want by its length, compared to all the other threating needles. Our smallest threading needle, the 10 to 20# size, has a length of 5.3". Each larger threading needle is .1" longer than the last, with our largest 400 to 500# size being 6.5" in length. When we started, we spent a year gathering all of the requested features for our new needles. Having some way to identify the threading needle sizes was one that was requested many times. Due to their size and materials, the length was the only way to address this request. The primary size of the threading needle is the ID, or Internal Diameter, indicating the approximate size of the mono/fluoro line that it will fit inside. The threading needle size you need is determined by the size of the mono/fluoro line you are using. The ID sizes of our threading needles can vary up to .002" due to the Stainless Steel Hypodermic tube manufacturing process. This is the standard acceptable size variance of the SS tubes we use to make our needles. As we receive new shipments of needles, the IDs may change up to this .002" size. It is recommended that you select a needle that is at least .002" larger than your line for ease of use. It can also be difficult to fit an exact size of line into a needle. If you have a problem with your line not fitting into one of our needles, please send us an email and we will analyze and resolve the problem. Model Description TubeLength OD Size ID Size* Spectra Sizes N02017 10 to 20# Small Threading Needle 5.3" .025"/.635mm .017"/.430mm up to 60# N03020 20 to 25# Small Threading Needle 5.4" .028"/.710mm .020"/.510mm up to 80# N04023 30 to 40# Small Threading Needles 5.5" .032"/.810mm .023"/.580mm up to 80# N05026 40 to 50# Threading Needle 5.6" .036"/.900mm .026"/.670mm 60 to 130# N06032 50 to 60# Threading Needle 5.7" .042"/1.06mm .032"/.810mm 80 to 130# N08038 60 to 80# Threading Needle 5.8" .050"/1.27mm .038"/.960mm 100 to 300# N10042 80 to 100# Threading Needle 5.9" .050"/1.27mm .042"/1.06mm 100 to 300# N13047 100 to 130# Threading Needle 6.0" .058"/1.48mm .047"/1.19mm 130 to 300# N15053 130 to 150# Threading Needle 6.1" .065"/1.65mm .053"/1.35mm 200# and up N20060 150 to 200# Threading Needle 6.2" .072"/1.83mm .060"/1.50mm 200# and up N30067 200 to 300# Big Threading Needle 6.3" .083"/2.11mm .067"/1.70mm 300# and up N40077 300 to 400# Big Threading Needle 6.4" .095"/2.41mm .077"/1.96mm 400# and up N50091 400 to 500# Big Threading Needle 6.5" .0109"/2.77mm .091"/2.31mm 500# and up