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Many tension and sewing related difficulties can be the result of not recognizing how the needle and thread work together.

In general:

1. Needle size refers to the diameter of the needle blade above the scarf in hundredths of a millimeter. A sewing machine needle with a blade diameter of .80 mm represents the size NM 80 and a needle with a diameter of 1.1 mm is NM 110. Therefore, the higher the needle number, the larger the needle size.

2. Thread size is based on two numbering systems: NE for English Numbering of cotton sewing thread and NM for Metrical Numbering of synthetic sewing thread. Opposite to needle numbering, the higher the number the finer the thread.

needle diagram

3. The sewing thread diameter should be about 40% of the needle size for proper loop formation (condition #1). In this situation, the threaded needle penetrates the fabric being sewn and the thread will slip into the long groove of the needle, reducing friction to a minimum as the thread goes through the fabric. The moment the short grove is through the material, the thread on that side of the needle will automatically be jammed between the side of the needle and the fabric and will be kept taut until the needle has reached its lowest point. As the needle starts its return, the thread in the long groove can easily glide within the groove, but the thread on the opposite side will be retarded and will form a loop. At this point (usually after the needle has traveled upward (about 2-3 mm) the different shuttle or hook systems slip through the loop and join the top thread with the bottom thread. This is how stitches are formed.

DIAGRAM 1 (cross section view)

Correct needle/thread

Sewing thread too thick
for needle size

Sewing thread too thin
for needle size

thread at 40

thread at plus 40

thread at minus 40




proper loop formation

If the needle/thread condition #2 occurs, the thread is jammed on both sides of the needle resulting in poor loop formation. (It appears like a loose upper tension or looping on the bottom of the fabric) The extreme friction will cause skipped stitches, thread breakage and tension problems. In condition #3, where the thread is too thin, the sewing thread is uncontrolled and the loops become irregular. This results in faulty stitches and damage of sewing thread. (wavy appearance, etc.)


-Visually observe the long groove and needle eye size difference between a size 70 (10) and size 90 (14) needle.

-Test sew on linen fabric:

  • First, try size 70 needle & size NM (polyester) size 50 / 60 thread
  • Next, try size 90 needle & size NM (polyester) size 50 / 60 thread.

There will be sewing problems associated with the first combination of thread and needle sizes.(It appears like a loose upper tension or looping on the bottom of the fabric.)



Needle Size

Cotton Thread (NE)

Silk Thread (NM)

Polyester Thread(NM)

Fabric Weight

Fabric Weight

Fabric Weight

European American light med heavy light med heavy light med heavy
60 8 80 80 - 200/3 160/3 140/3 200/3 160/3 150/3
65 9 - 80 70 120/3 120/3 120/3 140/2 140/3 120/3
70 10 70 60 50 120/3 100/3 80/3 120/3 100/3 80/3
80 12 60 50 40 100/3 70/3 60/3 120/3 100/3 70/3
90 14 50 40 36 100/3 70/3 60/3 100/3 70/3 60/3
100 16 40 36 30 70/3 60/3 50/3 70/3 60/3 50/3
110 18 36 30 24 60/3 50/3 40/3 50/3 40/3 30/3
120 20 30 24 20 50/3 40/3 30/3 40/3 30/3 20/3

Foot Note # 1

At Great Western SMS there is only one ratio that applies when a service is performed, we only use size 80/12 needles and when you look at the chart you will see that this size of needle is right in the middle of the range of needle sizes. You know also that as the needle size increases/decreases so does the "wire" size.

Therefore, during the course of an overhaul, various adjustments are made that are based on the needle size. If we were to service with a larger needle, then when the customer goes home and uses a much smaller needle size, then all of those tolerances will be greatly changed. If only the size 80/12 is used, then all of the other sizes will fall into tolerance. Since we use size 80/12 needle for servicing machines, we also only use size 120 polyester thread of good quality. Polyester is used only due to cost effectiveness when compared to using high quality cotton thread.

Foot Note # 2

If you experience difficulty threading the eye of the needle, then it is likely that the thread you are using is too big to fit well in the needle.

(In this case, you will then ALSO have a tension problem on your hands.)

This is also why on machines that are equipped with a needle threader (a small hook that pokes through the eye of the needle) the threader WILL become damaged (bent) and stop working. To use any built-in threader you must be using a needle size 80/12 or larger to allow for the "hook" of the threader to fit through the eye!! If using a smaller than size 80/12 needle then you will have to manually thread needle so as to avoid damage to parts!

Foot Note # 3

I have found through the years that Sewing Machine dealers don't know, or understand this important fundamental fact about the relationship between the needle and the thread (oh so very basic knowledge). This is why I often find that upper tension setting's (internal) are usually set much higher than they should be, so as to cover-up any apparent tension problem (looping on bottom of fabric). This tension problem usually corrected by simply using the correct needle/thread combination (unless further mechanical failure exists). As a general rule, 95% of upper tension dials have numbering of 0 - 9 on them, with a normal range of 3 - 5. As a check to YOUR machine; thread it as far as to the take-up lever (with the presser foot up, as this releases upper tension disks, to allow thread to fit completely between them) and then, lower the foot, and as you pull the thread from the take-up lever, and as you turn the dial toward the "0" position, the pressure on the thread weakens and when you get to the "0"position it becomes "0".

In many cases, you will STILL feel pressure on the thread when "0" is reached (tension is set high) or will feel the pressure disappear long BEFORE you reach "0" (tension is set low). If this check reveals that 0 does not equal 0, another fault elsewhere is likely being covered up by an internal tension increase or decrease setting!


I find that many machines come to me with the upper tension units set quite high (i.e.: 0=3) for one reason only; and that is to cover up the needle/thread size deficiency.

Hutterite colonies generally sew with a great deal of stretch material and use a stretch needle size 75. Usually matched to that needle is a size 40 - 70 polyester thread (low quality) that is used for ALL their sewing. As we refer to Needle/thread chart, first you see that a size 70 poly thread is correctly matched to a size 100/16 needle. If size 75 needle is used with size 70 poly thread then condition #2 of diagram 1 exists and will create looping on the underside of fabric. Increasing the upper tension setting WILL cover this up BUT, when the same machine is then set for heavier sewing, the first thing used is a LARGER needle, and if that is the case, the thread now fits correctly in needle. Now the increased upper tension setting results in the lower thread being drawn up! SO WHAT IS THE THING TO DO??

Simple, educate the customer to understand that the only correct thing to do is, first, have me set the internal upper tension setting to: "0" = "0". Then, when she wants to sew stretch fabrics with this thick thread (convincing Hutterite colonies to change to the correct thread is futile!) then she must turn the dial to a higher number to obtain NO looping on bottom, then, reduce to normal setting on heavy materials! (use the dial for what it does!) VIOLA!

Foot Note # 4

Occasionally I browse the newsgroups and forums on the web. What I commonly see is people with problems sewing, asking others for help. This is a great thing if the advice given is useful/helpful. One of the comments I see frequently is "did you change the needle?" I suggest that most of the time this advice is good BUT if the person is having the trouble due to a large size thread with a small size needle then if he/she changes the needle to the same size needle then nothing has changed! Send your friends here to my site for some lengthy, but hopefully, WORTHWHILE reading. Also, feel free to print off our needle/thread chart for your reference!



My next best piece of professional advice is this:

# 1 WHENEVER possible (ss sewing, quilting, stippling) attach and use the machines accessories; straight stitch presser foot/straight stitch needleplate! Although it is inconvenient to install and remove constantly, it WILL save you money in the long run (parts breakage/damage). It WILL increase your machine's performance dramatically


First, find a straw and place one end on a table and put pressure on the other end with your hand. The straw will flex and buckle. Now repeat the procedure but place your other hand in the middle of the straw forming a circle with your fingers joined to your thumb. Now the straw can flex and bend only so far because your hand is supporting it. This is what happens to a sewing machine needle as it moves up/down and pushes it's way through thicker material. It wants to flex and deflect (the heavier the fabric the worse). Using a straight stitch needleplate guides and limits the needle deflection!

With finer fabrics & materials, because the opening of the ZZ needleplate is wide, as the needle pushes its way through, it can tend to push the fabric down with it. The straight stitch needleplate supports the material well around the opening in which the needle enters, supporting it as it is being pierced by the needle.

In quilting: using the straight stitch needleplate, during " stippling ", this plate will limit the deflection of the needle through the free-hand movement and limit damage to the hook!

# 2 This deflection becomes "helped" by the incorrect use of presser feet.

Sewing (SS) with a zig-zag presser foot over seams causes more problems. As the presser foot goes up, the angle of the foot changes and the needle is then deflected off the rear edge of the presser foot opening, towards the front.

It is then that the needle will strike the front edge of the needleplate opening (polishing these nicks in the needleplate opening created by this deflection is very common in a sewing machine service and can only be polished so far before the opening is too large and plate replacement is necessary!)

NICKS IN ZZ PLATE (will cause thread breakage!)

As the foot goes down, the angle again changes, and now the needle deflects of the front of the foot and likely strikes the rear of the needleplate opening, as well as possibly the hook mechanism (nicks causing thread breakage)

What is important to note is that the "slot" of the regular zig-zag foot goes left to right. The "slot" of a straight stitch foot goes front to back. The "slot" of the straight stitch foot also will then guide the needle from left to right (like the straw experiment!) as it sews.

As a final thought, I have seen many a person who has just purchased a new expensive machine have many problems and complaints as to the sewing ability of her new machine. Often I have heard the comparison drawn to their OLD machine or her grandmothers old machine stating, "That old machine used to sew through anything!" Well, the old machine only did straight stitch and came only with a single hole plate and straight stitch presser foot! Now, new sewing machines with all the "bells and whistles" have come out and produce a much wider stitch then ever before! On top of this, when a computerized machine is first turned on, it assumes SS sewing position and the needle centers right in the middle of that wide opening.

This immediately brings failure we first talked about, being the needle pushing fabric down the hole.It is VERY important that the new machine you buy has the straight stitch plate and foot either as a standard accessory or available to purchase separately.