CHAPTER 20 ■ COUPLER
Testing the Cut Pieces
To make one coupler, you should now have three 22 mm long tubes of diameters^7 / 32 inch,^1 / 4 inch, and^9 / 32
inch. You should also have a 13 mm long tube of^3 / 16 -inch diameter.
Combine the three 22 mm long tubes by pushing the tubes into each other to form one thicker 22 mm
long tube (see far left of Figure 20-13). If any of the tubes don’t slide in easily, carefully sand the blocked tube
or replace any damaged tubes. Don’t worry if the tube lengths vary a little bit, and are not completely even.
You can either ignore it or sand the end down as a group.
Insert the 13 mm long tube into one end of the 22 mm long combined tube. Again, test for a smooth fit.
When satisfied, separate the tubes again (the end of a small screwdriver or the remaining stock of tubing
helps push the inner tubes back out).
LEGO Cross Axles
A LEGO cross axle is long thin black beam that looks like a plus sign (+) or the letter “X” when viewed from
the end. LEGO axles are designed to insert into the hubs of wheels, gears, and other LEGO parts. Although
the connection is achieved only by friction, the fit is firm and usually doesn’t shift or separate during use.
Selecting a LEGO Cross Axle Length
LEGO pieces are commonly measured in comparison to the number of studs on top of a standard LEGO brick.
For example, the cross axles in Figure 20-14 are 4, 5, and 6 LEGO units in length. (That translates to 31.8 mm,
39.7 mm, 47.6 mm.) LEGO cross axles are available in LEGO unit lengths of 2, 3, 4, 5, 6, 8, 10, and 12.
Figure 20-13. Left: Three 22 mm tubes inserted together (left side of left panel) placed beside a 13 mm tube
(right side of left panel). Right: 13 mm tube partially inserted to test the fit