Crimping Open Barrel Terminals

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I have just got a crimping tool and also the open barrel crimp terminals. The crimp terminals are—I think—clone of FASTON terminals, uninsulated 187 series straight receptacles from the premier line. The 187 series can be mated with 4.8 mm tabs. As an aside:

  • The 187 series name was from its tab size: 0.187 in = 4.7498 mm ≈ 4.8 mm.
  • Receptacles = female terminals.
  • Tabs = male terminals.

The crimping tool is TNI-U TU-03B.

I had never crimped using this tool and these terminals before, so I tought it would be prudent to practice. I found a piece of 20 AWG wire, and began the practice. At first I stripped about 1 cm of insulation, but I quickly found that it was excessive. Stripping 5 mm of insulation is ideal for these terminals. I tried fitting a terminal inside the crimping tool’s jaw, to choose which teeth/hole is suitable. For TU-03B, this 187 series receptables fit in the first hole/teeth.

First Try

I put the terminal too deep inside the crimping tools’s teeth. The result was a deformed terminal.

Off to a bad start, eh? I didn’t have beginner’s luck.

Second Try

This time some conductor strands were not crimped correctly.

This means less conductivity between wire conductor and the terminal. The protruding strands also could make unwanted contact with other conductors, possibly creating short.

Third Try

I stripped the insulation too short this time.

This kind of mistake would cause unreliable electrical connection between the wire conductor and the terminal.

Fourth Try

I didn’t see anything wrong this time.

To make sure I really got it, I want to try one more. I’ll call it done if the next try also succeed.

Fifth Try

I stripped the wire almost too short. But the conductor strands were at least flush with the edge of conductor crimp section of the barrel.

I made a mental note to actually use a ruler next time to make sure the insulation is stripped just right. For now I call this practice done.


  • I managed to crimp correctly starting from the fourth try. (Edit: I’m not sure anymore. See updates below.)
  • I should use a ruler to measure the correct length of insulation to strip.
  • This practice is done. (Edit: Need more practice. Or maybe not. See updates below.)
  • My phone’s macro capability suck.

See you folks.

2021-04-26 Update

I have just read The Good Crimping Guide by TE Connectivity. On page 15 of the guide, it said:

Bellmouth must be visible at wire end of wire barrel.

I had no idea what a bellmouth was. Good thing the guide has a picture at the same page.

My fourth and fifth tries—the ones I said “Great Success!!"—evidently have no bellmouth whatsoever. That means I still haven’t “got it” 😔.

2021-04-26 Update (Again)

I have just read the FASTON Terminals Insulated and Uninsulated catalog by TE Connectivity. On page 4 there is a picture of crimped straight receptacle terminal. On page 5 there is a picture of “F” crimp style. None have visible bellmouth.

Now I am confused. Both the guide and the catalog were made by TE Connectivity, but the picture in the catalog contradicts the guide.

To further the confusion, here’s another: Crimp Quality Guidelines poster, also by TE Connectivity. This one shows a picture of uninsulated straight receptacle, but doesn’t mention about bellmouths. At the next picture beside it, it shows a picture of a different type of terminal and then says:

Bellmouth must always be present

Does that means always present in all types of uninsulated terminals? Then why not also say that in the picture for the straight receptacle? Confusion all around.