FLC OF MLG ACR ACFT INADVERTENTLY DEVIATED FROM ASSIGNED TRACK DUE TO USING THE WRONG NAVAID FOR GUIDANCE.

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WHEN ASKED TO HOLD AT RANDOM FIX (HUB 234/70) WITH A 15 MIN LATER EFC; DIVERSION BECAME A REAL POSSIBILITY. WE WERE GIVEN AN INITIAL HDG OF 030 DEGS TO THE FIX; BUT I CONCURRED WITH CAPT THAT IT DIDN'T APPEAR TO BE AN INTERCEPT HDG. MEANWHILE; I WAS COORDINATING WITH OUR DISPATCHERS REGARDING CHANGING OUR ALTERNATE TO IAH TO GIVE US ANY HOLDING TIME AT ALL. DISPATCH REPLIED IAH WAS WORSE THAN HUB; AND TO DIVERT TO NEW ALTERNATE OF CRP AT EFC IF NOT CLRED TO PENETRATE. CAPT ADVISED ATC ENTERING HOLDING; BUT 'NOT ESTABLISHED YET ON 234 DEG RADIAL.' ATC REPLIED 'I SEE YOU IN A R TURN CORRECTING.' WE ALSO ADVISED ATC THAT WE WOULD HAVE TO DIVERT TO CRP AT THE EFC. THEY INSTRUCTED TO INTERCEPT 234 DEG RADIAL OUTBOUND AND THAT WE SHOULD BE ABLE TO LAND AT HUB. ATC WAS VERY BUSY METERING AIRPLANES INTO BOTH ARPTS AND WITH AIRPLANES DODGING TSTMS. AS WE WERE FLYING OUTBOUND TO INTERCEPT THE RADIAL; ATC GAVE US CLRNC TO GLAND (ON THE GLAND 7 ARR); THEN DIRECT HOBBY. I QUESTIONED THE ARR; SINCE I DIDN'T HAVE A 'GLAND 7' TO HOBBY. THEY THEN STATED GLAND WAS THE 234 DEG RADIAL AT 34 DME AND GAVE US AN INITIAL HDG OF 020 DEGS TO INTERCEPT. AGAIN; WE CONCURRED THAT IT WAS NOT AN INTERCEPT HDG AND ADVISED ATC. THEY THEN STATED 020 DEGS WOULD INTERCEPT THE HUMBLE 234 DEG RADIAL. WE DIALED UP IAH (116.6) AND THE 020 DEG VECTOR APPEARED TO BE CORRECT. (DSCNT AND LNDG WERE UNEVENTFUL.) WE REALIZED THAT OUR INITIAL CLRNC WAS PROBABLY TO THE IAH 234 DEG RADIAL AT 70 DME FOR HOLDING. WE NEVER DID A FULL TURN IN HOLDING AND TCASII DIDN'T SHOW ANY ACFT ON THE SCOPE DURING THE ENTIRE INCIDENT; SO ATC PROBABLY WAS NEVER AWARE WE WERE USING THE WRONG NAVAID. IN THE CONFUSION. WE WERE TASK SATURATED AND SO WAS ATC. THEY NEVER QUESTIONED OUR NAV THROUGHOUT THE INCIDENT. THE FACT THAT IAH (116.6) AND HUB (117.6) ARE SO CLOSE CONTRIBUTED TO THE PROB; AS WELL AS THE FACT THAT 'HUMBLE' AND 'HOBBY' SOUND VERY MUCH ALIKE. WE ARE NOT SURE WHETHER ATC GAVE US THE WRONG CLRNC OF WHETHER WE 'HEARD' THE CLRNC WE WERE EXPECTING.