[Jim McDougall]

Mandara was of course situated in what is now Cameroon, and the kingdom of Kanem-Bornu extended into these regions, including parts of Niger, Nigeria and Chad, with these regions all Sultanates . Muslim scholarship prevailed through these areas, however in many cases there were concerns over the nominal observance of Islamic Faith, which led to thre Fulani jihad in the 19th century against Mandara.

The fact that the Bornu state was founded by Arabs, Berbers and Hausa in the 14th century and the continued Sultancys in all of these regions, coupled with the prevalent Arab trade and scholarship in my opinion suggest that there was indeed powerful Arab influence present throughout. Although it has never been suggested that the takouba originated as a sword form in West Africa, it is acknowledged that its presence extends widely through the Sahara, most typically associated with the Tuareg.
The influences from the East are noted in certain scholarly references in which many takouba blades are termed, masri, which means Egyptian, loosely translated from the east.

The trade routes I have mentioned many times have resulted in many instances of sometimes unusual hybrid weapons, and carried influences as well. There are cases of triple channeled kaskara type blades mounted in rondel hilt type swords in Sierra Leone and other West African regions. These did not originate there, but the blades clearly arrived from the east, either from points of entry in the northern littoral or from trade inbound from Chad or Sudanese regions.

Regarding the inlaid copper or brass plug, I have discovered an interesting reference in which Dr. Lloyd Cabot Briggs discusses this phenomenon in his work on Tuareg swords and daggers (p.80). Referring to a takouba with intermediate (south or central) attribution, and with a blade that he notes could be European, he states , "...this blade has been pierced about 3/16 of an inch above its rounded point and the resulting hole is filled by a copper plug 3/16" in average diameter on the obverse and 1/4" on the reverse".
He claims another example has a similar hole, unfilled, and that he has no idea what the pierced mutilations might be for.

The point is of course, that the practice did exist in Saharan regions in at least some degree. The fact that the instances here relate to Tuareg swords, and they of course only nominally accepted Islamic Faith, does suggest non Arabic source was possible for the copper insert....unless one considers the profound presence of Islamic Faith throughout all of these regions, which influenced Tuaregs as well as many other tribal entities who were more devout followers within these Sultanates.

Addendum:

Just found another reference which might be of interest, though a bit ancient for direct influence on these swords, still pertinant to a curious practice:

"...Frankish pattern welded blades taper to a rounded point. When treatment of the blade is completed some of the blades are marked in the upper part with half moons or crosses of bronze or gold, and sometimes a nail of gold is hammered into a hole in the blade".
H.R. Ellis-Davidson noting the al Kindi ref.

This information begs the question, just how old is the broadsword tradition in North Africa? and could these ancient practices have been brought into tribal regions during the early occupations there? It would appear that the Arab world did know of the Frankish practice.....since this reference was from al-Kindi.

Things to ponder.