So, this doesn't really fit the topic, but it sort of does.
Wiktionary (which is pretty brilliant on this topic) lists 22 light u-stems in Proto-Germanic. (that is: nouns ending -uz or -u, with a short vowel in an open syllable in the root).
Of those 22... four, nearly 20%, are words for pointy sticks (posts, spikes, spears, etc)! And all four begin with sC-clusters. [from the other direction: 4 out of 12 u-stems with initial sC clusters are words for pointy sticks!] This seems way too much to be a coincidence! But it also doesn't seem obvious how they could all be related.
[and another of the 22 is also a word for sticks]
spaluz could conceivably be related to staluz. But spituz and speru seem harder to fit in.
Beyond the u-stems, there's also spitan and spito (presumably just reanalysed variants), and likewise steluz, stelô and stalô, as well as sperru and sparru. While spiro is theoretically unrelated. But there's also stakaz, and stalukaz (that one's probably a derivationg of staluz), and speutan, and stauraz, and skaftaz, and then over with the meaning 'splinter' (smaller pointy stick) there's speldan, and splinton and spelk and spilaz, none of which are allegedly related. So in various parts of England today, a splinter can be called a 'splinter', a 'spilk', a 'speld', a 'spill' or 'spile', or a 'spale', all of which are theoretically unrelated in etymology, but they really don't look it!
These all seem too similar to be coincidence, but also a bit too varied to fall under the usual sound-symbolism thing.
Actually, here's a good crosslinguistic one:
English: spit, a skewer for food
Norwegian: spyd, a skewer for food
Not related! Theoretically!
And more solidly in English: spale (strengthening cross-timber, or lathe) and pale (wooden post, or cheese scoop). Unrelated - one is from Germanic 'spaluz', while the other is from Latin 'palus', with more or less the same meaning as one another.