When it comes to machine hair strokes for eyebrows, many PMU artists use stroke machines (also called wireless rotary pens) daily. However, not all artists fully understand the concept of stroke length and how it affects pigment implantation and overall results. In this article, we’ll break down the meaning of stroke length, its impact on your work, and how to choose the right one for your technique.
What Is Stroke Length in a PMU Machine?
In simple terms, stroke length refers to the distance the needle moves in and out of the skin with each cycle of the machine. It is generally equal to or greater than the needle depth, meaning it determines how deep the pigment can penetrate the skin.
Common stroke lengths on the market range from 2.5mm, 2.7mm, 2.9mm, 3.5mm, and 4.0mm. Any stroke length above 4.0mm is typically considered more suitable for tattoo machines rather than PMU.
How Stroke Length Affects Pigment Implantation
Because the skin is elastic, the actual depth the needle reaches is often slightly less than the machine’s maximum stroke length. Different skin types also react differently to needle penetration due to varying levels of elasticity and tightness.
Key Characteristics of Stroke Lengths:
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Shorter Stroke (2.5mm - 2.9mm):
- Provides lighter impact on the skin.
- Ideal for creating soft, low-saturation hairstrokes.
- Suitable for artists with a naturally heavier hand pressure.
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Medium Stroke (3.5mm - 4.0mm):
- Delivers a stronger impact and implants pigment more efficiently.
- Best for higher saturation hairstrokes.
- Recommended for artists with a lighter touch to ensure proper pigment retention.
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Longer Stroke (Above 4.0mm):
- Typically used in traditional tattooing rather than PMU.
- Can be too aggressive for delicate PMU work, leading to over-saturation, pigment migration, or blue-gray healed results.
Why You Shouldn’t Just Choose the Longest Stroke Length
Some artists assume that using the longest stroke length with the highest power setting will result in faster, more saturated strokes. While this may seem logical, it often leads to over-saturation, uneven pigment retention, and poor healing results.
Think of it like dropping a stone from different heights:
- Dropping a stone from the 10th floor (short stroke length) will have a controlled impact.
- Dropping it from the 20th floor (long stroke length) will create a much stronger impact, potentially causing trauma to the skin.
When the stroke length is too long, the needle enters the skin with too much force. This can cause pigment to spread too widely beneath the skin, leading to blurring and discoloration.
How to Choose the Right Stroke Length for Your Style
Your hand pressure and speed are key factors in determining the best stroke length for you.
- If you have a heavy hand, opt for a shorter stroke length (2.5mm - 2.9mm) to prevent over-saturation.
- If you have a very light hand, a slightly longer stroke length (3.5mm - 4.0mm) may help achieve better pigment retention.
- If you’re unsure, start with a medium stroke (3.0mm - 3.5mm) and adjust based on results.
Adjusting Power & Speed for Different Stroke Lengths
The higher the stroke length, the lower the recommended speed setting.
General Power & Speed Guidelines:
- 4.0mm Stroke → Lower speed (1-2 settings)
- 3.5mm Stroke → Medium speed (3-3.5 settings)
- 2.5mm Stroke → Higher speed (3.5-4 settings)
However, these are just reference points—your ideal settings should also be based on your hand speed, technique, and experience level.
Why Technique Always Comes First
No matter what machine, stroke length, or power setting you use, the most important factor is your technique. Machines and settings are just tools—your skill as an artist determines the final outcome.
By understanding stroke length, pigment implantation, and machine power, you can adapt your technique and create beautiful, precise, and natural-looking hairstrokes.