a fly on the coach-wheel

English as a Second Language English Vocabulary, Grammar and Idioms
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Would you tell me whether I am right about my interpretation of the expressions in bold in the following sentence?

Come! Confess, both of you! You were only flies on the wheel. (B. Show, “Back to Methuselah”)

a fly on the coach-wheel = nonentity, a person laying one’s significance on thick

Thanks for your efforts.