Updating Column With Info - String Or Binary Data Would Be Truncated

I wrote this query to pull some information involving 3 tables dbo.NewFamNbrs$, dbo.CGIItemMaster and dbo.CGIFamilyMaster. In addition I want to perform an update statement to update column dbo.CGIItemMaster.FamilyIDX with the information of dbo.CGIFamilyMaster.IDX. I also know that truncation is indicating that I'm trying to insert data into a field not large enough. So I performed a len() function on the both columns and order by desc and they both came up with 4 as being the max.

Query:

SELECT a.PART, a.Family, b.FamilyIDX, c.FamilyID, c.IDX
FROM dbo.NewFamNbrs$ a LEFT OUTER JOIN dbo.CGIFamilyMaster c ON a.Family = c.FamilyID LEFT OUTER JOIN dbo.CGIItemMaster b ON a.PART = b.PART

Results of query:

PART Family FamilyIDX FamilyID IDX
000127233TF011468 TF01 506
000129880TF011468 TF01 506
003110 MET061468 MET06 1915

UPDATE STATEMENT:

begin tran
update dbo.CGIItemMaster
set FamilyIDX=c.IDX
FROM dbo.NewFamNbrs$ a LEFT OUTER JOIN
CGIFamilyMaster c ON a.Family = c.FamilyID LEFT OUTER JOIN
dbo.CGIItemMaster b ON a.PART = b.PART