Document And Entity Information - shares	9 Months Ended
	Jul. 03, 2021	Jul. 21, 2021
Document Information [Line Items]
Entity Central Index Key	0000764401
Entity Registrant Name	INSTEEL INDUSTRIES INC
Amendment Flag	false
Current Fiscal Year End Date	--10-02
Document Fiscal Period Focus	Q3
Document Fiscal Year Focus	2021
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jul. 03, 2021
Document Transition Report	false
Entity File Number	1-9929
Entity Incorporation, State or Country Code	NC
Entity Tax Identification Number	56-0674867
Entity Address, Address Line One	1373 Boggs Drive
Entity Address, City or Town	Mount Airy
Entity Address, State or Province	NC
Entity Address, Postal Zip Code	27030
City Area Code	336
Local Phone Number	786-2141
Title of 12(b) Security	Common Stock (No Par Value)
Trading Symbol	IIIN
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		19,357,571