Choosing Your Microstop Countersink Cage

To choose a microstop countersink cage, work through four choices in order: the cutter, the series, the shank and the footpiece. This guide covers each one, with the Wescon series that fit common aircraft jobs.

Countersinking is the process of preparing a hole so a fastener sits flush with the surface. A microstop countersink cage, also written micro stop, controls how deep the cutter goes. Depth control keeps fastener rows flush on the metal and composite panels of aircraft wings and fuselages, so the surface stays aerodynamic.

A countersink that is too deep or too shallow keeps the fastener from seating correctly. Over time, this weakens the joint and can cause panels to separate.

A microstop, also called a countersink cage, attaches to a handheld drill motor, holds the countersink cutter at a fixed setting, and helps control the travel depth of the cutter to a set length. Once set, it holds that depth across hundreds or thousands of holes without drifting. This consistency is why microstops are the standard tool aerostructure engineers use for countersinking work.

CCPhoto: Wescon Industries Inc., CC BY 4.0

Choosing the right microstop depends on a few parameters your job demands.

How to Choose Your Microstop

Step 1. Determine the Correct Cutter

CCPhoto: Wescon Industries Inc., CC BY 4.0

The main purpose of the microstop is to hold a cutter meant for countersinking; the cutter that’s in use is one of the main factors that will help you identify which microstop can hold it. For that reason, you need to choose the right cutter. What you need to know are:

• The dimensions of the fastener or countersink rivet, since they determine the cutter needed to create a countersunk hole where the fastener sits flush with the surface.
• The material of the work surface or aerostructure panel, since it determines the material of the cutter required
• The installation standards or specifications for the job

Our microstops can hold:

• Imperial threaded cutters with 10-32, 1/4"-28, 3/8”-24 or 7/16”-20 threads
• Metric threaded cutters with M6x1, M8x1 or M10x1 threads

Step 2. Determine the Correct Series

Fasteners sit in different places. Some are easy to reach; others might be in tight or obscure areas. Because of this, no single microstop configuration works for every job. The right series depends on your access to the jobsite.

CCPhoto: Wescon Industries Inc., CC BY 4.0

Once you know your cutter and the microstop use case, you can choose the right skirt option. Some skirts have a limit on the cutter size they can hold.

Step 3. Match Your Shank to Your Drill Motor

Not every drill motor used for countersinking is the same. That is why microstops come with different shank options. Based on your drill's chuck type, you can choose between:

• Round (Blank): A standard shaft that fits a standard 3-jaw chuck.
• Tri-Flat (TF): Also fits a 3-jaw chuck, built for heavy countersinking on steel and larger cutters, where applications require better grip; preferred in situations where a round shank might slip in the chuck.

A Quick-Change (QC) configuration is also available. It needs a QC chuck adapter, such as our WES1750 Series, mounted on a threaded drill motor. This system mostly applies if you work at a Boeing facility or as a Boeing subcontractor, where it is the standard.

Long threaded shank (TSL) options are also available. However, these are custom-built for threaded motors or chucks upon request.

Step 4. Protect the Work Surface with the Right Footpiece

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Every Wescon series, with its cutter thread and shank options, is in the microstop countersink cage catalog.