BL-123 Precision Steel 1-2-3 Block Review

What are 1-2-3 Blocks

1-2-3 blocks are precision ground, rectangular blocks that measure 1″ x 2″ x 3″.  They are often used to align work on a milling machine table.  They can also be used as a right angle guide to ensure work is oriented at 90 degrees.  In addition to the 1-2-3 block dimensions, there are also other sizes including 2-4-6.  Precision blocks can be solid or have holes pre-drilled and tapped for bolting to a table or to work.

Blocks in their protective wooden box. An old cigar box worked perfectly. Click the image to purchase the blocks from Amazon.

The BL-123 Blocks

I recently ordered the BL-123 brand of 1-2-3 blocks for my mini-mill setup.  I am very happy with them so far.  The price was low and the quality great.  Let’s take a look at the un-boxing and measuring of the blocks.


Lots of layers means good protection. The blocks were shipped in a small padded envelope.  Inside, they were in a thick plastic bag.  Inside the plastic bag is a light cardboard box.  Inside the cardboard box is the typical machinery oil paper.  Inside the oil paper…is a single block.  I found no damage to the blocks.  Great!

This is the item packaging that was inside the padded shipping envelope.

The blocks were also packaged in this thin cardboard box.

Thin plastic covering and oil paper wrap for each block.

Blocks by themselves.


Of course, the most important aspect of any precision item is how precise it is.  The manufacturer indicates that these blocks are perfectly square with an accuracy of 0.0002″.  Using my digital caliper which can only measure to 0.0005, I went to work getting a sense of the accuracy of these blocks.  They were dead on according to the limits of my caliper.

Block 1 Measurements

Block 2 Measurements

Mounting Holes

5 of the holes are tapped for 3/8″ 16 TPI bolts.  The other holes are clear and measure .3565 which just barely allows an 11/32″ test rod to pass.  The configuration of the holes allows for easy mounting to a mini-mill table.


The surfaces of the blocks are ground with a surface grinder and have an excellent look and feel.  It appears that the edges have been ground by hand, which was a little disappointing from a look and feel perspective, but does not affect the accuracy or usefulness of the blocks.


Overall, I am very pleased with these 1-2-3 blocks.  I don’t often use them, but for the price and precision they are very important to have in the shop.