Nested query needed?

No syntax, no result either...

Create Table Cust_Tbl(item int, CURRENT_CUST char(3), MAJOR_MODEL char(3),
MINOR_MODEL char(5), MODEL_SERIAL_NBR char(5),
MODEL_NBR char(8), CUST_DELIVERY_STATUS char(10),
PART_NBR char(20), MODEL_QTY char(3))
insert into Cust_Tbl
select 1,'ABC','M3','8','38619','ZA453','Active','1006927-110',197 UNION
select 1,'ABC','M3','9','38629','ZB374','Active','1006927-110',38 UNION
select 1,'ABC','M3','9','38618','ZB365','Active','1006927-110',38 UNION
select 1,'ABC','M3','8','38614','ZA456','Active','1006927-110',197 UNION
select 1,'ABC','M3','8','60629','ZA459','Active','1006927-110',197 UNION
select 1,'ABC','M3','8','38609','ZA450','Active','1006927-110',197 UNION
select 1,'ABC','M3','9','38622','ZB367','Active','1006927-110',38 UNION
select 1,'ABC','M3','9','38616','ZB362','Active','1006927-110',38 UNION
select 1,'ABC','M3','9','60627','ZB378','Active','1006927-110',38 UNION
select 1,'ABC','M3','9','38617','ZB363','Active','1006927-110',38 UNION
select 1,'ABC','M3','9','38626','ZB371','Active','1006927-110',38 UNION
select 1,'ABC','M3','8','38615','ZA457','Active','1006927-110',197 UNION
select 1,'ABC','M3','8','38611','ZA452','Active','1006927-110',197 UNION
select 1,'ABC','M3','8','38612','ZA454','Active','1006927-110',197 UNION
select 1,'ABC','M3','9','38627','ZB372','Active','1006927-110',38 UNION
select 1,'ABC','M3','8','38610','ZA451','Active','1006927-110',137 UNION
select 1,'ABC','M3','9','38630','ZB375','Active','1006927-110',38 UNION
select 1,'ABC','M3','9','38628','ZB373','Active','1006927-110',38 UNION
select 1,'ABC','M3','9','38632','ZB377','Active','1006927-110',38 UNION
select 1,'ABC','M3','9','38621','ZB364','Active','1006927-110',38 UNION
select 1,'ABC','M3','8','60631','ZA950','Active','1006927-110',197 UNION
select 1,'ABC','M3','9','38631','ZB376','Active','1006927-110',38 UNION
select 1,'ABC','M3','8','38613','ZA455','Active','1006927-110',197 UNION
select 1,'ABC','M3','8','60626','ZA458','Active','1006927-110',197 UNION
select 1,'ABC','M3','8','60630','ZA949','Active','1006927-110',197 UNION
select 1,'ABC','M3','9','38625','ZB370','Active','1006927-110',38 UNION
select 1,'ABC','M3','9','60628','ZB379','Active','1006927-110',38 UNION
select 1,'ABC','M3','9','38624','ZB369','Active','1006927-110',38 UNION
select 1,'ABC','M3','9','38623','ZB368','Active','1006927-110',38 UNION
select 1,'ABC','M3','9','38620','ZB366','Active','1006927-110',38
;with topsellers
as
(
Select PART_NBR, MINOR_MODEL, MODEL_QTY, item,
ROW_NUMBER() OVER (
PARTITION BY item
ORDER BY MODEL_QTY desc
) row_num
From Cust_Tbl
)

select * From topsellers where row_num = 1

good job, you see how long and how frustrating that was? When a person asks help and they do not provide usable data, good people on this site who are very busy might ignore your question.

So going back to your original question, the sample data you provided which columns are
Part Type, Model Type

My apology. I don't mean to cause any frustration or being disrespectful. I like help to be thinking through an issue, and not just given a solution. Need more time to think and repose the question. Thank you for your time.

No need for apology and no you did not cause frustration nor were you disrespectful