When to Use a Snap Cap vs. Screw Cap Tube

Damaged samples can cause researchers to lose valuable time in lab tests, especially in medical labs where time is of the essence. Lab personnel must have the correct instruments available to them in order for accurate testing to take place. While it might seem inconsequential, the right centrifuge tube cap can have a significant impact on the safety of your samples.

At Crystalgen Inc., we understand the considerations clinical laboratories must make to ensure safe, effective testing. This guide will explore how and why to choose the right vial and cap types for each protocol. It will also briefly discuss proper handling methods for both snap cap and screw cap tubes.

Understanding the Difference Between Snap Cap and Screw Cap Tubes

There are two primary types of tubes labs use to test materials — snap cap tubes and screw cap tubes. Knowing the difference between the two can help lab managers make more informed decisions when purchasing new lab equipment.

Snap Cap Tubes

Plastic snap cap tubes are the most common type of tube used in life sciences laboratories. They feature an attached cap that pops open and snaps shut. While they provide a suitable seal for most general-purpose applications, they are less secure than screw cap tubes in demanding processes.

Screw Cap Tubes

Screw cap tubes open and close using a simple screw mechanism. This feature provides a tight seal, as the top physically cannot pop off the tube. Some models also feature a silicone O-ring on the inside of the cap for additional protection against leaking or evaporation.

Snap Cap vs. Screw Cap Tubes in Laboratory Settings

Both tube types have distinct advantages and disadvantages based on which tests researchers use them for in the lab.

Advantages and Limitations of Snap Cap Tubes

Snap caps are significantly more convenient to use than screw cap tubes. Researchers can open and close a snap cap tube with one hand, enabling comfort and efficiency when processing high volumes of samples.

However, snap cap tubes are often less reliable in demanding environments. High pressure and heat can cause the tube to pop open during processes like centrifuging or autoclaving, resulting in ruined samples. Carefully matching the tube type to the application can help researchers prevent this problem.

Advantages and Limitations of Screw Cap Tubes

The main advantages of using a screw cap tube include:

• Greater durability: Because the cap and tube are separate pieces, there is no risk of the tube becoming damaged through repeated opening and closing.
• Tighter seal: Screw cap tubes provide a tighter seal than snap cap tubes, eliminating the risk of losing samples during high-intensity applications or long-term storage.
• Easier labeling: Screw cap tubes often come with an assortment of cap colors, allowing for easy differentiation between samples.

Note that screw cap tubes are often less convenient than snap cap tubes because they do not enable single-handed operation. Researchers must set the tube down or place it in a stand in order to fill or empty it. This extra step makes high-volume applications significantly more challenging.

There is also an increased risk of cross-contamination that can occur when a researcher accidentally switches caps between tubes. Although samples should never come into direct contact with tube caps, particles can still transfer from the air in the tube to the cap and contaminate it. Some models come with attached caps similar to snap cap vials.

Choosing the Right Equipment: When to Use Snap Cap vs. Screw Cap Tubes

The intended application is the most important factor in deciding when to use a snap cap tube or a screw cap tube. Pretesting with water-filled tubes can help researchers determine whether their tubes meet the requirements of their protocol. 

Ideal Uses for Screw Cap Vials

In addition to general-purpose lab applications, screw cap vials are a better fit for life sciences processes such as:

• Autoclaving
• High-spin centrifugation
• Long-term sample storage

Essentially, any protocol that requires high heat and pressure — or that causes a researcher to doubt the sample's integrity — should use a screw cap tube.

Optimal Uses for Snap Cap Tubes

The ease of opening and closing snap caps makes them ideal for use in general lab tests with large volumes of samples. This characteristic also makes them suitable for teaching laboratories in higher and secondary education, where schools go through massive quantities of lab consumables every year.

How Cap Types Impact Sample Integrity in Medical Laboratories

The type of cap used for a medical test may seem inconsequential, but it can have a significant impact on sample integrity. Snap caps create a less reliable seal than screw caps, which means samples are at more of a risk of becoming compromised in demanding environments than they would be in general-purpose applications.

Another critical consideration when purchasing screw cap tubes is ensuring that the caps fit the tubes. Some manufacturers sell them separately, which can cause lab managers to accidentally purchase incompatible pieces.

Safety Measures: Proper Use of Snap Cap and Screw Cap Tubes

As with any other type of lab equipment, personnel safety depends on knowing how to use centrifuge tubes properly. Regardless of which cap type a specific test requires, proper tube cleaning and maintenance protocols are critical for obtaining accurate results and keeping lab employees safe. 

Safety Guidelines for Snap Cap Tubes

Squeezing the sides of the tube until the cap pops open can cause the contents to fly out. Instead, researchers should place their thumbs underneath the cap's safety tab and gently push upward. To seal the tube, they simply have to press down on the center of the cap with their thumbs until it snaps closed.

Safety Guidelines for Screw Cap Tubes

To safely open a screw cap tube, a researcher should twist the cap open. If the cap is not attached to the tube, they must place it nearby to reduce the risk of cross-contamination. Once they have filled the tube or removed its contents, they then place the cap back on and twist it shut.

Buy Snap Cap and Screw Cap Tubes From Crystalgen

Ultimately, your choice of which tube to use depends on your research needs. Whether you're interested in snap cap or screw cap tubes, Crystalgen Inc. can help supply you with the right tools for the job.

Our years of experience in the industry have enabled us to become one of the world's most trusted lab equipment suppliers. Browse our selection of centrifuge tubes and other lab equipment to find the best materials for your application.